| Switching power converters are designed to transform available ac(dc) power sources to ac(dc) waveforms required by the load. The operation of switching power converters relies on the appropriate control of the semiconductor switches. Pulse-width modulation (PWM) serves to effectively perform the control of the semiconductor switches. However, the signal modulated by the conventional PWM scheme contains unwanted harmonics, which may cause electromagnetic interference, acoustic noise, and vibration in motor-drive applications. These effects are addressed with spectrum shaping so as to modify harmonic characteristics of PWM switching signals with minimal or no sacrifice of signal-band integrity.; A particularly useful approach involves the application of double Fourier integral analysis for selective harmonic elimination and electromagnetic interference suppression. Double-Fourier integral analysis has been used to study spectrum characteristics of standard PWM signals. In this thesis, the work on double Fourier integral analysis is extended to capture the mathematical nature of the spectrum shaping. A reference-based PWM scheme, the so-called predistorted PWM (Pd-PWM), is proposed which can provide high-quality switching signals to fulfill some of the spectrum-shaping tasks. In addition, frequency-modulated PWM (FM-PWM) is investigated. It shows potential for effectively implementing spectrum-shaping tasks as well.; The ultimate goal of spectrum-shaping technology is to provide the designer with the ability to specify a desired harmonic spectrum and then to realize it using a proper modulation scheme. The results of Pd-PWM and FM-PWM bring us one step closer to understanding how to meet this goal. |
