Two control schemes for PWM converters, average current-mode (ACM) control and charge control, are studied in this dissertation. The small-signal models are derived for continuous-conduction mode PWM converters employing these two controls. Sampled-data modeling is applied to the current loop modeling, and the obtained models are accurate up to half the switching frequency. The relationships between current loop instability and converter operating conditions for both controls are found for the first time. The derived models are verified by both time-domain simulations and experiments. The models can be used for both voltage loop and current loop analysis and designs. Comprehensive design guidelines for PWM converters with both controls are also provided. The small-signal characteristics of these two controls are compared with those of peak current-mode control. The applications of ACM control and charge control to power factor correction (PFC) circuits are studied. Charge control is applied to continuous-conduction mode flyback converter to achieve a single-stage PFC. The current loop instability in PFC circuit and its effect on the input EMI filter design are investigated. The trade-off between the current loop stability nlargin and line current distortion is also discussed. / Ph. D.