• Journal of Power Electronics
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• v.15 no.6
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• pp.1438-1445
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• 2015

A new DC-DC power converter is researched for renewable energy and battery hybrid power supplies systems in this paper. At the charging mode, a renewable energy source provides energy to charge a battery via the proposed converter. The operating principle of the proposed converter is the same as the conventional DC-DC buck converter. At the discharging mode, the battery releases its energy to the DC bus via the proposed converter. The proposed converter is a non-isolated high step-up DC-DC converter. The coupled-inductor technique is used to achieve a high step-up voltage gain by adjusting the turns ratio. Moreover, the leakage-inductor energies of the primary and secondary windings can be recycled. Thus, the conversion efficiency can be improved. Therefore, only one power converter is utilized at the charging or discharging modes. Finally, a prototype circuit is implemented to verify the performance of the proposed converter.

• The Transactions of the Korean Institute of Power Electronics
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• v.15 no.3
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• pp.207-217
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• 2010

Recently, the use of DC power increased due to the increased use of digital load. Power factor of input current decrease and input current harmonics increase, and conversion loss which is occurred in the AC / DC converter is a problem to provide the proper DC voltage to the device equipped with an internal AC / DC converter. Hybrid system supplies the AC power and DC power to AC load (motor load and the transformer load) and DC loads (computers, TV, LED fluorescent light) at the same time it supplies the renewable energy and utility energy taken power from Utility to user for improving the efficiency and renewable energy improvements in ease of use. This paper studies DC characteristics of traditional AC load for Hybrid distributions.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.10 no.9
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• pp.4145-4164
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• 2016

Energy harvesting is an increasingly attractive source of power for cellular networks, and can be a promising solution for green networks. In this paper, we consider a cellular network with power beacons powering multiple mobile terminals with microwave power transfer in energy beamforming. In this network, the power beacons are powered by grid and renewable energy jointly. We adopt a dual-level control architecture, in which controllers collect information for a core controller, and the core controller has a real-time global view of the network. By implementing the water filling optimized power allocation strategy, the core controller optimizes the energy allocation among mobile terminals within the same cluster. In the proposed green energy cooperation paradigm, power beacons dynamically share their renewable energy by locally injecting/drawing renewable energy into/from other power beacons via the core controller. Then, we propose a new water filling optimized green energy cooperation management strategy, which jointly exploits water filling optimized power allocation strategy and green energy cooperation in cellular networks. Finally, we validate our works by simulations and show that the proposed water filling optimized green energy cooperation management strategy can achieve about 10% gains of MT's average rate and about 20% reduction of on-grid energy consumption.

• Proceedings of the KIPE Conference
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• 1999.07a
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• pp.423-426
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• 1999

This paper describes a driving scheme of the series hybrid electric vehicle that we have developed. Both series HEV and parallel HEV are well known. We chose series HEV because it provides good energy efficiency in urban driving and operates in all-electric mode in performance. And engine-Generator is driven at constant speed with constant load to maintain the low emission. And the battery supplies power during high-load and receive energy during low-load

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.1196-1199
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• 2017

A series-hybrid power system was designed for quad-tilt prop UAV and the characteristics was analysed. The power system consists of a 4.5kW rotary engine-generator and a li-battery as power sources, a power controller manages the overall power and supplies to the vehicle system. The output power of the engine is to be matched with the generator performance considering mechanical driving loss and generating efficiency, and also loss for charging and discharging of the battery energy. It is applied that the constant speed operation of the engine-generator to minimize overall fuel consumption by integrating the generating power and the battery energy, consequentially the battery capacity and characteristics could be important factors for improvement of the system efficiency.

• Journal of the Korean Solar Energy Society
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• v.27 no.1
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• pp.47-54
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• 2007

Interests on renewable energy are increased due to oil price and environmental problems aroused from the fossil energy usage. In this study, performances of a solar assisted hybrid heat pump system are analyzed by experimental method. The developed system could runs at two types of operating mode. When the storage temperature is higher than the set temperature, the stored hot water in storage tank is supplied to the load directly. On the other hand, when the storage temperature lower than the set temperature, the water inside of the storage tank is used as heat source of the heat pump. In this study, the system control temperature for the alternation of the operating mode is set to $40^{\circ}C$ of the storage tank outlet. As results, it is founded that the COP of the developed heat pump system shows between 3.0 and 3.5. It is resonable performance for the heating system with a renewable energy as secondary heat source. The solar collect used in this study could supplies heat to the storage tank at over 400 W/m2 solar intensity. If the irradiation is lower than the 400 W/m2, the circulation pump stored and it could not supply heat to the storage tank. It is found that the difference temperature between the outlet of the storage tank and collector is $3^{\circ}C$. Even though, the extended study should be conducted to get a optimum performance of the developed system with various operating condition and control strategies.

• Clean Technology
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• v.26 no.1
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• pp.65-71
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• 2020

Various solar hybrid energy conversion processes, which have both the advantages of renewable energy sources and fossil energy sources, have been developed in the world because stable and predictable energy supplies, such as electricity and natural gas, are necessary for modern societies. In particular, a solar hybrid energy conversion process based on a dual fluidized bed process concept has been expected as the promising solution for sustainable energy supply via thermochemical conversions, such as pyrolysis, combustion, gasification, and so on, because solar thermal energy could be captured and stored in fluidized bed materials. Therefore, the attrition and heat transfer characteristics of silicon carbide and alumina particles used for fluidized bed materials for the solar hybrid energy conversion process were studied in an ASTM D5757 reactor and a bubbling fluidized bed reactor with 0.14m diameter and 2m height. These characteristics of novel fluidized bed materials were compared with those of sand particles which have widely been used as a fluidized bed material in various commercial fluidized bed reactors. The attrition resistances of silicon carbide and alumina particles were higher than those of sand particles while the average values of heat transfer coefficient in the bubbling fluidized bed reactor were in the range of 125 ~ 152 W m^-2K^-1.

• Transactions of the Korean Society of Automotive Engineers
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• v.11 no.5
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• pp.170-175
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• 2003

A control algorithm is developed for highly efficient operation of auxiliary power unit (APU) that consists of a diesel engine and a directly coupled induction generator in series hybrid electric Bus (SHEB). In a series hybrid configuration the APU supplies the electric power needed for maintaining the state of charge (SOC) of the battery unit in various conditions of vehicle operation. As the rotational speed of generator does not depend on the vehicle speed, an optimized operation of engine-generator unit based on the efficiency map of each component can be achieved. The output torque of diesel engine can be controlled by the amount of fuel injection, and the power converted from mechanical to electrical energy can be adjusted by generate control unit (GCU) using the decoupling vector control of torque and flux. As for the given reference of the generating power, the multiply of speed and torque, many combinations of operating speed and torque are possible. The algorithm decides the new operating point based on the engine efficiency map and generator characteristic curve. During the transition of operating points, the speed controller saturation is avoided using variable limit and filtering of generator torque reference. A test rig and SHEB consist of a 1.5L diesel engine and a 30kw induction generator are constructed by Hyundai Motor Company.

• Journal of Electrochemical Science and Technology
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• v.7 no.1
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• pp.41-51
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• 2016

In the stratosphere, the air is stable and a photovoltaic (PV) system can produce more solar energy compared to in the atmosphere. If unmanned aerial vehicles (UAVs) fly in the stratosphere, the flight stability and efficiency of the mission are improved. On the other hand, the weakened lift force of the UAV due to the rarefied atmosphere can require more power for lift according to the weight and/or wing area of the UAV. To solve this problem, it is necessary to minimize the weight of the aircraft and improve the performance of the power system. A regenerative fuel cell (RFC) consisting of a fuel cell (FC) and water electrolysis (WE) combined PV power system has been investigated as a good alterative because of its higher specific energy. The WE system produces hydrogen and oxygen, providing extra energy beyond the energy generated by the PV system in the daytime, and then saves the gases in tanks. The FC system supplies the required power to the UAV at night, so the additional fuel supply to the UAV is not needed anymore. The specific energy of RFC systems is higher than that of Li-ion battery systems, so they have less weight than batteries that supply the same energy to the UAV. In this paper, for a stratospheric long-endurance hybrid UAV based on an RFC system, three major design factors (UAV weight, wing area and performance of WE) affecting the ability of long-term flight were determined and a simulation-based feasibility study was performed. The effects of the three design factors were analyzed as the flight time increased, and acceptable values of the factors for long endurance were found. As a result, the long-endurance of the target UAV was possible when the values were under 350 kg, above 150 m² and under 80 kWh/kg H₂.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.1
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• pp.31-36
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• 2012

Military vehicles, compared to conventional vehicles, require higher driving performance, quieter operation, and longer driving distances with minimal fuel supplies. The series hybrid electric vehicle can be driven with no noise and has high initial startup performance, because it uses only a traction motor that has a high startup torque to drive the vehicle. Moreover, the fuel economy can be improved if the vehicle is hybridized. In series hybrid electric vehicles, the electric generation system, which consists of an engine and a generator, supplies electric energy to a battery or traction motor depending on the vehicle driving state and battery state of charge (SOC). The control strategy determines the operation of the generation system. Thus, the fuel economy of the series hybrid electric vehicle relies on the control strategy. In this study, thermostat, power-follower, and combined strategies were compared, and a 37% improvement in the fuel economy was implemented using the combined control strategy suggested in this study.