The doctoral thesis is devoted to study frequency-modulated (FM) switch-mode power converters (SPC) and to improve their quality. This includes both improving effectiveness of the use of FM for increasing EMI attenuation and reducing the negative effect of FM on the main characteristics of SPC, such us output voltage ripples, efficiency and input power quality. FM SPC have been studied theoretically, experimentally and using computer simulations. In the doctoral thesis, formerly unknown causes of the increase in the output voltage ripples, deterioration of the input power quality and the efficiency of regulated FM SPC in both continuous conduction and discontinuous conduction modes are revealed. Original recommendations for reducing the output voltage ripples, improving the input power quality and increasing the efficiency of FM SPC are proposed and verified. A procedure for the calculation of the output voltage ripples and the efficiency in FM SPC is also developed. The results obtained and the recommendations proposed could be applied for designing high-quality FM SPC as well as for their development. The doctoral thesis is written in Latvian, contains introduction, three chapters, conclusions, references, 9 appendices, 108 figures, 144 pages in total. A list of references consists of 122 sources.