Hsuan-Yu Yueh’s research while affiliated with National Taiwan University of Science and Technology and other places

The LLC resonant converter has been widely used in the power supply industry, such as server power, TV power, and adapter, because this converter can realize the zero-voltage switching (ZVS) at the power mosfet s of the primary side. Thus, the switch losses can be decreased, and the conversion efficiency can also be improved. The electric vehicle (EV) charger has been recently widely used in research and development. However, designing LLC resonant converters for the wide battery voltage range is difficult because this converter is usually utilized in pulse-frequency modulation (PFM) to regulate the output voltage. This converter will also be limited to the low operating frequency range for the high conversion efficiency due to the switching frequency. By contrast, the phase-shift modulation (PSM) control for the wide output voltage range has been used at LLC resonant converters. However, the ZVS will be lost due to the lagging leg of the LLC resonant converter when the phase-shift angle is remarkably excessive. The burst-mode control has also been proposed for the converter to regulate the output voltage and maintain high conversion efficiency at light-load conditions. Therefore, this article utilized the combination of PFM, PSM, and burst-mode control for the LLC resonant converter operating at the wide output voltage range for EV charge applications. Furthermore, this article proposed a synchronous rectification advance on-time control for PFM control, which can help address the ZVS at the lagging leg when the phase-shift angle is excessive. Detailed analysis and design of this control method are also described. The performance evaluation of the proposed LLC resonant converter with hybrid control was finally realized under the following conditions: 3.75 kW, dc input voltage of 400 V _DC , dc output voltage of 75–475 V _DC , and maximum conversion efficiency around 97%.

The LLC converter has been widely used in the power supply industry for its high conversion efficiency. When the output load is low, the LLC resonant converter will substantially increase the operating frequency, thereby reducing the conversion efficiency and exceeding the limited operating frequency of the specification. Thus, burst-mode control is applied to increase the ability of regulation at light-load conditions. Even so, the switching period of power switches still occurs at a high switching frequency. Burst-mode control will also result in an extremely low-frequency output voltage ripple. In this study, a valley switching control (VSC) for the LLC resonant converter at light-load conditions is proposed. The VSC control strategy maintains the output voltage by modulating the pulsewidth signals of drivers and achieves valley switching by modulating the switching frequency. Thus, the VSC strategy can reduce the operating frequency compared with the frequency modulation strategy. Compared with burst-mode operations, the proposed VSC effectively reduces the switching loss and has the advantage of high-frequency output voltage ripple. The VSC increases the efficiency and the power quality of the converter. Detailed analysis and design of the proposed method are described. Experimental results are recorded for a prototype converter with a dc input voltage of 400 $V_{\mathrm {DC}}$ , an output voltage of $48~V_{\mathrm {DC}}$ , and an output current of 12.5 A.

This study presents the topology of a three-phase LLC resonant converter with matrix transformers. The three-phase LLC resonant converter has the advantages of conventional LLC resonant converters, including zero-voltage switching at the primary side, zero-current switching at the secondary side, high-frequency feasibility, and high efficiency. Moreover, it has additional advantages that differ from conventional LLC, including low output capacitor current ripple, natural current sharing in three resonant currents, and a high power level. As a result of the above mentioned characteristics, LLC topology has been used in many electric vehicle charging systems, server power systems, and other high-power applications. However, as the power level becomes higher and higher, the input voltage is usually too high to reduce conduction loss, and the output current also increases. This situation makes transformer design more difficult. The increasing current means more core and copper loss, and the heat dissipation of the transformer becomes more difficult. Matrix transformer technology can improve this problem directly and simply. By utilizing matrix transformers, which are primary series connected and secondary parallel connected, the primary voltage stress and secondary current stress of the transformers can be reduced, and the output current can be distributed. The analysis of the proposed converter in this study includes a circuit operation introduction, a time-domain analysis, calculation of the transfer ratio curve in the frequency domain, and a loss analysis. The theoretical analysis and performance of the proposed converter are verified. A three-phase LLC resonant converter with matrix transformers prototype is built with a high input voltage of 800-VDC and high output current of 200-A. The output voltage is 100-VDC. The waveform and efficiency data will be shown in the experimental results.

This paper presents the designed method and the implementation of stepped air-gap ferrite inductor applied in power factor correction (PFC). Conventionally, the input inductor of the PFC has a designed consideration on the maximum output power; thus, designing the PFC for peak-power-load conditions results in a very large inductor. The proposed designed method improves the load-carrying capability without increasing the volume of the inductor when the PFC is operating in peak-power-load conditions. The stepped air-gap ferrite inductor maintains the inductance in the rated-full-load and sustains the peak-power-load conditions with the lower inductance. Compared with the conventional ferrite inductor, the proposed method can maintain the size and the efficiency of the power supply, and promote the power-carrying ability. The detailed analysis and the design of the proposed method are described. Experimental results are recorded and evaluated by a prototype PFC with an AC input voltage of 110–264 VAC and a DC output voltage of 384 VDC. Finally, the volume of input inductor is kept with 40950 mm ² , the efficiency is also same compared with the conventional inductor, and the load-carrying capability of the converter is promoted from the normal rated power of 1 kW to the peak power load of 2 kW.

Recently, three-phase series-resonant converters (SRCs) have been proposed for high power applications. Three-phase SRCs can achieve zero-voltage-switching (ZVS) of the primary power switches and regulate the output voltage by pulse-frequency modulation. The interleaving technique is also a conventional method for DC-DC converters to achieve a high power level, reducing the output voltage ripples due to operating out of phase at the same frequency between the two converters. However, an interleaved three-phase SRC cannot easily synchronize switching instants between the two modules due to the component tolerances of circuits. In the proposed control method, phase shift modulation (PSM) is used to solve the output current imbalance caused by component tolerances. The power switches of the converter can also maintain synchronizing switching instants between the two modules. Therefore, the lower output voltage ripple can be achieved. A detailed analysis and design of this new control method for interleaved three-phase SRCs are described. Finally, prototype converters with a 2.4 kW total output were built and successfully tested to verify the feasibility of the current sharing modulation.

This letter presents a current‐controlled variable magnetizing inductance of transformer for further improving the holdup time on half‐bridge LLC converter. When the input voltage is failed, the magnetizing inductance of transformer can be decreased sharply; therefore, the LLC converter holdup time can be improved without adding additional auxiliary circuit. The mathematic model between magnetizing inductance and step‐gap structure of transformer is proposed, and the benefit effects using this step‐gap structure of transformer have been verified in this letter. Finally, a 180‐W, LLC converter utilizing step‐gap structure of transformer has been achieved, and detailed analysis and design of the proposed step‐gap structure are described. This letter presents a current‐controlled variable magnetizing inductance of transformer for further improving the holdup time on half‐bridge LLC converter. When the input voltage is failed, the magnetizing inductance of transformer can be decreased sharply; therefore, the LLC converter holdup time can be improved without adding additional auxiliary circuit. The mathematic model between magnetizing inductance and step‐gap structure of transformer is proposed, and the benefit effects using this step‐gap structure of transformer have been verified in this letter. Finally, a 180‐W, LLC converter utilizing step‐gap structure of transformer has been achieved, and detailed analysis and design of the proposed step‐gap structure are described