PUBLICATIONS

 Favored for power conversion systems, the PWM (Pulse Width Modulation) schemes have been widely employed to generate switching pulse patterns. However, PWM (Pulse Width Modulation) control signals have a drawback in that their power spectrum tends to be concentrated around the switching frequency and the resulting harmonic spikes cause an EMI (Electromagnetic Interference) and switching losses in semiconductors, etc. In order to remove these undesirable effects and suppress these harmonic spikes, RPWM (Random Pulse Width Modulation) schemes have been developed. They have proven effective, and a number of realization techniques have been reported. However, they are complex and require various hardware components, such as multiple timers. Thus, the configuration of the conventional RPWM is quite complicated. In this thesis, CDSDM (Combined Dither Sigma-Delta Modulation) is proposed as a more effective RPWM scheme for power switching converters. The proposed scheme has a simple digital implementation, which comprises a first-order SDM and a random dither generator. SDM (Sigma-Delta Modulation) is a type of switching modulation used to reduce these harmonic spikes, and several SDM schemes are investigated. The first-order SDM produces a switching pulse pattern that has the same lowfrequency component as the reference input. In the DSDM (Dithered SDM), the SDSDM (Space-Dithered Sigma-Delta Modulation) and TDSDM (Time-Dithered Sigma-Delta Modulation), the signals are classified by the location of their random dither additions. The random dither disperses the switching frequency of the output pulse waveform, which results in the reduction of harmonic spikes. The relationship between the harmonic spectra and sampling numbers per switching cycle is studied. The algorithms of the CDSDM are executed in a DSP controlling a buck converter. In experimental setup, the random switching pulse pattern is generated using the DSDM and the suppression effect of harmonic spike is confirmed through a spectral analysis of the measurements of the load voltage. In these schemes, the switching frequency is spread by a random dither generator placed on the input or the output parts. Experimental results are presented where the advantages of the new proposed CDSDM are confirmed by applying to a buck converter.