In the no load condition, LLC converter usually fails to regulate its output voltage although it operates at a high switching frequency. Till now, it is hard to obtain the exact relationship between design parameters and the maximum switching frequency for no load regulation capability. In this paper, a specific criterion for no load regulation of LLC converter is provided, without using active components or other modulation schemes. By analyzing the macroscopic switching period and microscopic switching transition in the no load condition, it is shown that not only the peaking resonant current during the switching transition, but also the resonant tank design affect the no load regulation of LLC converter affect the no load regulation capability. Furthermore, the relationship among design parameters are analyzed and design guideline is also provided to achieve no load regulation at the specified maximum switching frequency. To verify the effectiveness of the proposed design, 400V input and 50V/200W output prototype is built and tested.

With rapid developments in the satellite data services market, the demand for low Earth orbit (LEO) satellites is increasing. Advancements in designing lightweight satellites are essential to maximize profits from the mass production of LEO satellites in private companies. This paper proposes a new direct charging control suitable for electrical power systems for lightweight and highly reliable LEO satellites. Moreover, an analysis of the proposed solar array regulator (SAR) in terms of weight, efficiency, and reliability is presented. Additionally, the advantages of the proposed SAR in terms of lifespan and state of health (SOH) of Li-ion batteries are presented because the peak value of the battery charging current and the temperature changes during the battery charging operation are relatively small.

This paper proposes high efficiency three-level dc-dc converter with reduced circulating current and rectifier voltage stress by using coupled inductor in the rectifier circuit. Because of decreased circulating current, the conduction loss in the primary circuit is reduced. In addition, since the rectifier diodes with low forward voltage drop can be employed due to the small voltage stress, the conduction loss of rectifier diodes can be reduced. Therefore, the efficiency can be increased due to the reduction of the conduction losses in the primary circuit and rectifier diodes. The characteristics of the proposed converter are analyzed and compared with other three-level converters. The validity of the proposed converter is verified by the experimental results of the prototype with 540-600 VDC input and 750W (48 V/15.625 A) output.

Due to the problem of global warming caused by greenhouse gas emissions, internal combustion engines in a lot of transportation systems are being electrified. For the railroad propulsion system, it is essential to apply a high-voltage/large-capacity energy source in order to ensure that the system operates properly. Thus, fuel-cell and rechargeable battery systems are being considered nowadays. The battery system can receive and store all regenerative energy to improve energy efficiency. In addition, since the battery pack of a propulsion system utilizing a hydrogen fuel-cell requires continuous charging/discharging, regardless of the railroad vehicle’s driving profile, the battery pack is designed to ensure its stable use and to minimize maintenance costs. Consideration should be given to the characteristics of railroad vehicles. In this research, a hydrogen fuel-cell hybrid railroad vehicle propulsion system specification, which has been studied recently, was applied to study the considerations in the design of high-voltage/large-capacity battery packs for railroad vehicles. In particular, the passive and active cell-balancing circuit and an algorithm for the stable management of battery packs for hybrid railroad vehicles in which a continuous charging/discharging operation is repeated are proposed and verified through experiments.

Electronic devices usually operate in a variable loading condition and the power transfer efficiency of the accompanying wireless power transfer (WPT) method should be optimizable to a variable load. In this paper, a reconfigurable WPT technique is introduced to maximize power transfer efficiency in a weakly coupled, variable load wireless power transfer application. A series-series two-coil wireless power network with resonators at a frequency of 150 kHz is presented and, under a variable loading condition, a shunt capacitor element is added to compensate for a maximum efficiency state. The series capacitance element of the secondary resonator is tuned to form a resonance at 150 kHz for maximum power transfer. All the capacitive elements for the secondary resonators are equipped with reconfigurability. Regardless of the load resistance, this proposed approach is able to achieve maximum efficiency with constant power delivery and the power present at the load is only dependent on the input voltage at a fixed operating frequency. A comprehensive circuit model, calculation and experiment is presented to show that optimized power transfer efficiency can be met. A 50 W WPT demonstration is established to verify the effectiveness of this proposed approach.