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This paper proposes an improved zero current detection for critical conduction mode (CRM) control, which can compensate the input current distortion caused by the signal propagation delay and the existence of the negative resonance current. A unified variable on-time calculation method is also proposed to unify the formulas under the zero-voltage-switching condition and the valley-switching condition. Since these two methods are dependent on the boost inductance and device junction capacitance, which may be different from the nominal values, effort is needed to compensate the deviation on these two parameters. In this paper, an online monitoring method is proposed to compensate the numerical deviation. The proposed method only needs to sense the input voltage, output voltage, and the reverse flow time of the inductor current, leading to a high power quality in the entire input and load conditions. The experimental results of the proposed methods are demonstrated on a 200-W GaN-based CRM boost power factor correction prototype. With the proposed methods, the input current total harmonic distortion is only 0.78% at 110 VAC input with full load and 2.1% at 220 VAC input with full load. [ABSTRACT FROM AUTHOR]

This paper proposes an adaptive look-up-table (LUT)-based variable on-time (VOT) control for CRM boost PFC converters, which combines advantages of conventional LUT method and real-time calculation method. By the numerical fitting method, the approximate functional form of the on-time is derived, which is related to both the input voltage and load. The mapping relationships of VOT tables under different load and input RMS voltage are investigated. Based on the mapping relationships, only one VOT table is required to be preloaded in LUT. The adaptability of the proposed control is conveniently realized within the universal ac input and entire load range through the inherent voltage loop and a simple linear calculation. With the proposed control, the required memory space for VOT tables is effectively reduced and the computation time is significantly shortened, leading to a low system cost. Moreover, compared with the constant on-time control and other VOT controls, the proposed control can further suppress the input current distortion. The experimental results of an 160-W universal ac input prototype are built to verify the effectiveness and advantage of the proposed control. With the proposed control, the input current THD is only 0.97% at 110 Vac input with full load and is limited within 2.9% at 220 Vac input with full load. [ABSTRACT FROM AUTHOR]