Single-stage boost-LLC ac-dc converters have been a popular soft-switched topology because of the high-efficiency and being cost-effective. However, low power capacity is its main disadvantage. In this article, a novel single-stage interleaved boost-LLC ac-dc converter with higher power capacity is presented while achieving the low input current ripple. However, it still suffers from the wide and high bus voltage for universal operation, as a result of the conventional pulse frequency modulation (PFM) with the duty cycle of 0.5. Furthermore, this wide bus voltage will bring the difficulties in designing the LLC resonant cell. To solve these issues, a dual-loop feedback control strategy based on PFM/interleaved asymmetric pulsewidth modulation hybrid modulation and power balance based optimal design are proposed. With the proposed control strategy and optimal design, the bus voltage of the studied converter is not only significantly reduced, but also zero voltage switching for the primary switches and zero current switching for the secondary diodes are still maintained. Thus, the higher efficiency can be achieved. Operation principles and control scheme for the studied converter are fully addressed. The optimal design based on power balance principle is also discussed in this article. A 300 W prototype is fabricated to validate the theoretical analysis and optimal design. The experimental results demonstrate the prototype can simultaneously obtain the universal operation with high power factor above 0.98 and the quasi-constant bus voltage below 500 V. The measured peak efficiency is 92.7% under 115 Vac input voltage at full load.

The LLC Resonant converter is widely used in on-board charger applications for its high efficiency. However, conventional LLC converter with pulse-frequency-modulation suffers from a wide switching frequency range for realizing constant current (CC) and constant voltage (CV) charges. To address this problem, different from the traditional solution, a novel LCL resonant converter operating at a fixed resonant frequency with inherent CC and CV output characteristics is proposed in this letter. In the proposed concept, the CC and CV charges are accomplished by the special LCL tank. With the increasing of battery voltage during charging process, the resonant tank of the proposed converter is equal to the conventional LCL tank and LC tank for CC mode and CV mode, respectively. Thus, the sensing and control circuits are canceled while the wide zero-voltage-switching operation for primary switches and zero-current-switching for secondary diodes still be maintained. Therefore, the fixed resonant frequency operation, high efficiency, high reliability, and low cost are key features of the proposed converter. A 1-kW prototype with 400 V input and 250–400 V output is built and tested. The full load efficiency of 96.7% and higher than 96% for the CC mode were both achieved. The experimental results demonstrate the advance and validity of the proposed converter.

Due to the applied pulse frequency modulation control and switch integration, single-stage boost- LLC ac/dc converters suffer from high bus voltage, which makes them difficult to operate for high voltage input. To solve this issue, a novel single-stage ac/dc converter by incorporating the interleaved discontinuous conduction mode (DCM) boost cell and an LLC cell is proposed. Different from the existing topology, in the proposed converter, two capacitors employed for splitting the ac input voltage into two parts are placed before the rectifier bridge. Thus, the voltage across each power factor correction (PFC) cell is halved and the bus voltage can be significantly reduced. Furthermore, two high-frequency diodes and one filter capacitor are omitted, which helps improve the zero-crossing distortion of the input current. More importantly, the circuit efficiency is thus increased. Hence, low bus voltage, low component count, and high efficiency are the main advantages of the proposed converter. Simulations and experimental results are presented to prove the aforementioned features of the proposed converter.

To target the 80 Plus 380 Vdc Titanium specifications, this article proposed a novel fixed-frequency isolated dc–dc converter with full-range zero voltage switching (ZVS). Different from the conventional phase-shift full-bridge (PSFB) converter, the series capacitor structure and series-connected two transformers are incorporated in the proposed converter to achieve full-range ZVS operation and light-load efficiency improvement. First, the voltage stress of three primary switches is reduced to half of the input voltage because of the special series capacitor structure. Correspondingly, the energy needed for obtaining the ZVS operation of all primary-side switches is reduced by one-fourth of conventional methods. Furthermore, the employed series-connected two transformers not only achieve the full-range ZVS operation but also eliminate an output inductor presented in conventional PSFB converters. Therefore, higher efficiency can be achieved. In conclusion, low voltage stress, full-range ZVS operation, and fixed switching frequency are the main advantages of the proposed converter. A 360–440 V, 12 V/50 A prototype is built to verify the claimed features of the proposed converter. Experimental waveforms show the ZVS operation under the entire range. The measured efficiency is higher than 95% from 14 A load up to full load, and the peak efficiency of 96.7% can be achieved for 360 V at 25 A load.

Different from the widely used high-voltage (HV) inductive power transfer (IPT) systems, the low-voltage IPT systems with HV input suffer from the following challenges: the high output current brings high conduction losses in the secondary side, especially at the receiver coil; and the HV conversion ratio, such as 400 V input and 24 V output, results in the difficulties in designing the compensation parameters and loosely coupled transformer. To overcome these issues, a novel IPT topology is proposed in this article by incorporating the series-capacitor full-bridge (SCFB) inverter and inverse coupled current doubler rectifier. Thus, the following three improvements are achieved: first, the voltage stress of three primary switches is reduced to half of the input voltage because of the special series capacitor structure. Second, the inherent one-fourth voltage conversion ratio is achieved and reduced greatly the difficulties in designing the compensation parameters. Third, the current flowing through rectifier circuit is reduced to half of conventional full-bridge rectifier. Furthermore, the LC-LCC compensation is employed for matching the proposed SCFB topology while a novel parameter optimization method is proposed to improve the conversion efficiency. To demonstrate the claimed features of the proposed solution, a 1.2 kW IPT prototype with 400 V input, constant voltage 24 V output is built and tested. The measured efficiency curve indicates that the efficiency from 8 to 50 A load keeps above 94.5% and peaks at 96.63%.

Compared with conventional boost-LLC single-stage ac–dc converters, single-stage converters integrating buck–boost type power factor correction (PFC) and LLC cell can greatly reduce the bus voltage. However, the published buck-boost type single-stage converters remain the drawbacks of wide bus voltage range for universal input and limited output power range, and have raised concerns of high number of power devices and employed rectifier bridge. Different from the conventional solutions, to simultaneously achieve the universal-input and whole-load operation with reduced component number, low and constant bus voltage, a novel semi-bridgeless single-stage ac–dc converter is proposed by integrating the semi-bridgeless cascaded buck–boost PFC cell and half-bridge LLC resonant cell. Meanwhile, optimal design of the bus voltage for achieving the discontinuous conduction mode or boundary conduction mode operation is performed. furthermore, the DCX operation of LLC cell and simple control with fixed switching frequency are achieved because of the special circuit configuration, which greatly reduces the design difficulty of the LLC cell. The experimental results through an 85–265 V input, 12 V/25 A output prototype demonstrate a constant bus voltage of about 264 V, a peak efficiency of 92.0%, and PF values above 0.989.