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The use of single-stage power-factor-corrected (SSPFC) three-level resonant ac/dc converters solves many problems that present SSPFC converters face today, namely, high component stresses, high circulating currents, and low efficiency. This makes single-stage three-level resonant ac/dc converters a good candidate for high-power applications. These converters provide the flexibility of simultaneously using two control variables. They can operate with a combined variable-frequency and asymmetrical pulsewidth modulation or with a combined variable-frequency phase-shift modulation. This provides good regulation of the output voltage, dc-bus voltage, and input current. The drawback of these methods is that the efficiency of the converter drops as the load is reduced because the converter starts to drift away from its resonance frequency, thus leading to more circulating currents and conduction losses. Therefore, a load-adaptive energy storage technique is proposed in this paper to guarantee the converter operation near its maximum efficiency point for a wide range of loading. This leads to almost constant converter efficiency from full load to 40% load. The use of interleaved converters is also proposed to extend the constant efficiency range of operation to lighter loads (15%–20% of full load). Analytical simulation and experimental results are presented to verify the proposed methods. [ABSTRACT FROM AUTHOR]

This article presents a new three-level full bridge resonant single stage AC/DC converter. The converter is operated with a variable frequency pulse width modulation controller (PWM). A PWM is used to provide the required input current shaping as well as regulating the DC-bus voltage, whereas variable frequency control is used to tightly regulate the output voltage. Zero voltage switching (ZVS) is achieved for all switches. The proposed topology can operate with either continuous or discontinuous input current while maintaining high power factor. Owing to ZVS operation, reduced component stresses and low circulating currents the proposed converter has high conversion efficiency making it suitable for higher power operations compared to existing single stage AC/DC topologies as well as operating with universal input voltage. Operation, analysis and performance of the converter will be presented in this article. [ABSTRACT FROM AUTHOR]

In this paper, the performance of different three-level resonant converters is studied for single-stage power factor correction operation. These converters are suitable for power ranges higher than that in the currently available single-stage converters, due to their high efficiency and reduced component stresses. All the converters presented here are characterized by their ability to regulate the output voltage as well as the dc bus voltage. This leads to lower voltage stresses, wider input voltage range, higher output power applications, and improved efficiencies compared to existing single-stage topologies. Due to the availability of more degrees of freedom in the presented converters, two types of control strategies can be used for this purpose: variable frequency asymmetrical pulsewidth modulation control and variable frequency phase-shift modulation control. Three resonant converters will be studied in this paper and their performances as well as the applicability of the aforementioned control methods for each converter are compared. A 2.3-kW, 48-V converter with input voltage range of 90265 Vrms is used to study the performance of each case. [ABSTRACT FROM AUTHOR]