Modified Harmonic Current Control and Load Range Extension Method for Single-Stage Isolated DCM Boost AC–DC Converter

Single-stage discontinuous-conduction mode (DCM) boost ac–dc converters garnered significant attention for their low cost, high efficiency, and reduced bus voltage. However, the harmonic current control performance of the input current of these converters employing traditional schemes can still be improved. In addition, due to the DCM operation of the input inductor currents and the boost power factor correction (PFC) topology, this type of converter has an inherent power limitation. Exceeding the power threshold can lead to the bus voltage dropping below the input voltage, resulting in pronounced distortion in the input current. In this article, a single-stage two-switch ac–dc converter is introduced, and an input current PFC control method with variable feedforward parameter is proposed to suppress the odd harmonic current while facilitating soft-switching operation. Moreover, to address the power limitation of the traditional schemes, a load range extension method is proposed, in which a proper design of the input filter capacitance causes grid-side resonance in LC when the power is relatively high, and thus improves the operating load range, preventing the input current distortion due to excessive output power. Finally, a 500-W prototype is built to verify the feasibility and effectiveness of the proposed method.