In this paper, a high-efficiency DC/DC converter with low voltage stress is designed for green power applications. The proposed non-isolated high step-up DC/DC converter combines the advantages of switched capacitors, coupling inductors, and voltage multiplier techniques. Adding the cells of the switched capacitor not only increases the voltage gain but reduces the voltage stress of the semiconductor devices. High voltage gain can be achieved by adding a coupled inductor method to adjust the turns ratio. When these are combined with a voltage multiplier circuit, the leakage energy of the coupled inductor is recirculated to the output terminal with lossless passive clamping performance. The leakage inductance of the coupled inductor controls the current dropping rate of the output diode turn OFF so that the reverse-recovery problem is mitigated. The proposed converter integrates these three techniques to achieve high voltage gain without operating at maximum duty cycle. In addition, switching loss reduction is realized through zero current switching turn ON soft switching performance with low voltage stress of semiconductor devices. Finally, this paper verifies the performance of the proposed converter for theoretical analysis by using a 35~45V input, 380V output, and 1kW power prototype circuit.

In this paper, a new type of interleaved high step-up converter including a coupled inductor is proposed. The proposed converter has an interleaved configuration on the input side to reduce the ripple of the input current and increase the power level. Moreover, a stacked structure on the output side provides a high input/output (I/O) voltage gain. In addition, the proposed converter can avoid an extreme duty cycle, causing larger conduction losses, by combining a coupled inductor and a lossless clamp circuit with an interleaved method. These increase the efficiency by making the semiconductor device a low voltage stress and allowing the use of components with low voltage ratings. Also, the energy stored in the leakage inductor in the coupled inductor can be recycled to the output side, the MOSFETs can be partially ZCS turned ON, and the diode reverse recovery problem can be alleviated. Finally, a laboratory prototype circuit with an input voltage of 24V, an output voltage of 400V and an output of 500W was implemented to demonstrate the performance of the proposed converter.

The high-pressure gaseous hydrogen (HPGH2) storage method is widely used owing to the low density of hydrogen gas at ambient temperature and atmospheric pressure. Therefore, rigorous safety analysis of the filling and discharging of compressed gas in a hydrogen tank is required to achieve reliable operational solutions for the safe storage of hydrogen. In this study, the behavior of compressed hydrogen gas in a hydrogen tank was investigated for its discharge. Numerical models for the adaptation of gas and turbulence models were examined. Gas model effects were examined to account for hydrogen gas behavior at the discharge temperature and pressure conditions. Turbulence model effects were analyzed to consider the accuracy of each model: the assessment of the turbulence models was compared in terms of the turbulence intensity. From the study of gas model effect, the Redlich–Kwong equation was found to be one of the realistic gas models of the discharging gas flow. Among the turbulence models, the shear stress transport model and Reynolds stress model predicted the compressed gas behavior more accurately, showing a lower turbulence intensity than those of the realizable and renormalization group models.

This article is a study of bidirectional DC/DC converter for the energy storage systems. Non-isolated interleaved bidirectional high step-up/down (NIBH) DC/DC converter consists of a coupled inductor and a switched capacitor. The NIBH converter has important features such as low ripple current on the low voltage side, low cost, low component count, high voltage conversion ratio, low voltage stress, and soft switching operation of switches. Two coupled inductors are connected in parallel to the low voltage side to have low ripple current and increase the turns ratio to achieve high step-up/step-down voltage gain. The switched capacitors can be stacked in series with the high voltage side to achieve high voltage gain, and the active clamp circuit enables the switches to reduce conduction and switching losses with low voltage stress and soft switching operation. To verify the theoretical analysis and performance of the proposed converter, a 650W prototype circuit was implemented in the laboratory.

In this article, we deal with the onboard fast energy conversion system (FECS) that is installed in a wireless railway train (WRT), which receives electrical energy not from the wayside device but from the onboard device when traveling between stations, after getting such energy stored by fast charging during its stopping time at a station. The adopted input-series and output-independent architecture and the interleaving topology can reduce the size and weight of onboard FECS for 1500 V, which is double the operating voltage of the existing 750 V operating voltage. This allows 1200 V class insulated-gate bipolar transistor applications to increase switching frequency and reduce passive component volume. In addition, in order to secure system stability, which is important in any transportation system, a WRT must operate on the basis of simple control. Through a simple and efficient balance control based on a variable current limiter, the input voltage unbalance caused by the input voltage sharing is resolved. Also, it can control charging and discharging based on the energy moving characteristic of the train operation pattern and connection with a high-power energy storage pack. The performance of the onboard FECS at 1500 V with the proposed method is experimentally verified on a 600 kW prototype system.

Due to the low density of hydrogen gas under ambient temperature and atmospheric pressure conditions, the high-pressure gaseous hydrogen storage method is widely employed. With high-pressure characteristics of hydrogen storage, rigorous safety precautions are required, such as filling of compressed gas in a hydrogen tank to achieve reliable operational solutions. Especially for the large-sized tanks (above 150 L), safety operation of hydrogen storage should be considered. In the present study, the compressed hydrogen gas behavior in a large hydrogen tank of 175 L is investigated for its filling. To validate the numerical approach used in this study, numerical models for the adaptation of the gas and turbulence models are examined. Numerical parametric studies on hydrogen filling for the large hydrogen tank of 175 L are conducted to estimate the hydrogen gas behavior in the hydrogen tank under various conditions of state of charge of pressure and ambient temperature. From the parametric studies, the relationship between the initial SOC pressure condition and the maximum temperature rise of hydrogen gas was shown. That is, the maximum temperature rise increases as the ambient temperature decreases, and the rise increases as the SOC decreases.