This paper presents a methodology to deal with the control design for PWM converters in dc-to-dc power conversion systems. The concept of uncoupled dc-to-dc converter is established, which allows dc-to-dc converters to be designed independently from the source and load impedances. The control design strategy of the uncoupled dc-to-dc converters is formulated to offer good and robust closed-loop performance when the converters are coupled with the actual source and load subsystems. A peak current-mode controlled buck converter is used as an example throughout this paper to verify the proposed control design technique. We compare the control design of the uncoupled dc-to-dc converters with that of the converters coupled with resistive and non-resistive loads. The validity of the conventional design intended for a resistive load is also be discussed.