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It is essential to retain improved efficiency in a dc–dc converter over a wide load current range to extend the battery-life in portable devices. This requires a multi-mode controller, consisting of pulse-width-modulation (PWM) and pulse-frequency-modulation (PFM) schemes. However, existing approaches attempt to integrate structurally different controllers; thus it is difficult to achieve a seamless controller transition. While a digital platform offers controller configurations, it remains difficult to identify a suitable digital PWM/PFM technique and decide on its sampling mechanism to achieve stable behavior. This paper proposes a unified digital PWM/PFM scheme which shares a common digital PWM (DPWM) block and has the provisions for online controller configuration and automatic (switching) frequency adaptation. The proposed scheme retains improved efficiency over a wide operating range and inherently achieves seamless controller transitions. Further, a unified discrete-time framework is proposed for the analysis and design of the proposed multi-mode controller. Buck and boost converter prototypes are tested and the proposed controller is implemented using a field-programmable-gate-array device. [ABSTRACT FROM AUTHOR]

Active pulse-width-modulated (PWM) voltage rectifiers are commonly used to convert ac power from a three-phase grid to a regulated dc voltage with unity input power factor. The output voltage regulation is normally achieved by an outer voltage feedback loop and a sinusoidal pulse-width-modulated (SPWM) inner current loop. Due to output voltage disturbances, such as those produced by a capacitive load, the inner current loop can be easily driven into over-modulation and possible six-step operating regions. Current research efforts have focused on extending the linearity of the modulated voltage in the over-modulation range to reduce the input current harmonics and on studying the closed-loop stability via conventional small-signal linearization around a fixed operating point. Such linear techniques obviously fall short of predicting large-signal transient stability. In this paper, catastrophic bifurcation of the three-phase voltage-source converter is reported. The physical origin of the phenomenon is identified. Boundaries of catastrophic bifurcation in the parameter space are derived. The phenomenon has been verified experimentally. [ABSTRACT FROM PUBLISHER]