• The Transactions of the Korean Institute of Power Electronics
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• v.25 no.6
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• pp.477-483
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• 2020

This study proposes a DQ synchronous reference frame model of a series-parallel tuned inductive power transfer (SP-IPT) system. The wireless power transmission system experiences control difficulty because the transmitter-side controller cannot directly measure the receiver-side load voltages and currents. Therefore, a control-oriented circuit model that shows the dynamics of the IPT system is required to achieve a well-behaved controller. In this study, an equivalent circuit model of the SP-IPT system in a synchronously rotating reference frame is proposed using the single-phase DQ transformation technique. The proposed circuit model is helpful in modeling the dynamics of the voltages and currents of the transmitter- and receiver-side resonant tanks and loads. The proposed circuit model is evaluated using frequency- and time-domain simulation results.

• Journal of Power System Engineering
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• v.18 no.2
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• pp.25-30
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• 2014

In this paper, the heat transfer coefficient and pump consumption power of indirect refrigeration system using $CO_2$ as a secondary refrigerant were investigated experimentally. First, from the comparison of pump consumption powers of existing brines(EG, PG, EA etc.) and $CO_2$ as secondary refrigerants at the same experimental conditions, PG and $CO_2$ show the highest and lowest power, respectively. Second, the heat transfer coefficient of $CaCl_2$ is the highest, but PG is the lowest among other secondary refrigerants. From the above results, it is confirmed that $CO_2$ as the secondary refrigerant has excellent characteristics when comparing to existing brines. Thus, it is concluded that $CO_2$ is applicable as the secondary refrigerant of indirect refrigeration system.

• Journal of Magnetics
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• v.21 no.4
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• pp.652-659
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• 2016

In this study, the efficiencies for both the angular aligned and unaligned positions of the receiver and transmitter coils of wireless power transfer (WPT) systems are examined. Some parameters of the equivalent circuit were calculated with Maxwell 3D software. The analytical solution of the circuit was calculated in MATLAB program through the composition of the system's mathematical modeling. The numerical solution of the system, however, was calculated using PSIM, which is circuit simulation software. In addition, with the use of the finite element method (FEM) in Maxwell 3D software, transient analysis of the three-dimensional system was performed. The efficiency of the system was estimated through the calculation of input and output power. The results demonstrated that power was efficiently transmitted to a certain extent in aligned and unaligned positions. The results also revealed that, for aligned positions, high efficiency with air gaps of 15-20 cm can be obtained and that the efficiency quickly dropped with air gaps of more than 20 cm. For spatially unaligned positions, it was observed that wireless power transfer could be realized with high efficiency with air gaps of up to 10 cm and that efficiency quickly dropped with air gaps of more than 10 cm.

• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.2
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• pp.78-83
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• 2019

In this study, we analyze the structure of the transceiver coil in the inductive power transfer (IPT) system. In the IPT system, the transceiver coil design needs to have the highest magnetic coupling possible because of the relatively low magnetic coupling due to the large gap of distance without the core. The transmitting coil may be formed as a multi-layer type according to the distance between the transmitting and receiving coils if the receiving coil is configured as a multi-layer type on the inner structure of the receiving apparatus, thereby improving the magnetic coupling and system efficiency. We compare and analyze the coil magnetic coupling, and system efficiency according to the layer structure of the transmitting and receiving coils and verify the analysis by JMAG simulation. Experimental results show that the layer structure of the transceiver should be considered according to the inner space of the receiving device and the spacing distance.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.41 no.6
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• pp.415-421
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• 2017

As stricter environmental regulation have led to an increase in the water treatment cost, it is necessary to quantitatively study the input power of the aeration process to improve the energy efficiency of the water treatment processes. The objective of this study is to propose the empirical correlations for the mass transfer coefficient with the gas hold-up and input power in order to investigate the mass transfer characteristics of the aeration process. It was found that as the input power increases, the mass transfer coefficient increases because of the decrease of gas hold-up and increase of Reynolds number, the penetration length, and dispersion of mixed flow. The correlations for the volumetric mass transfer coefficients with gas hold-up and input power were consistent with the experimental data, with the maximum deviation less than approximately ${\pm}10.0%$.

• Journal of Energy Engineering
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• v.26 no.4
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• pp.57-66
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• 2017

Since the heat is not as fast as the electric power and the loss is relatively large compared to the electric power, it is not realistic to operate the thermal transfer system with on operation center like electric power trading. In the case of the Korea District Heating Corporation, where all the thermal transfer are currently being made, only two or four adjacent heat-generating power plants are being the heat trading. Therefore, In this paper, we concluded that it is appropriate to divide the integrated operation center for heat trading into several regions, to operate the hub integrated operation power plant in each region to reflect the characteristics of the heat medium and proposed the thermal transfer mechanism among integrated energy operators. Then, we have developed an algorithm that can optimize the heat transaction for the proposed mechanism and applied it to the actual operators to verify the usefulness of the proposed algorithm.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.25 no.10
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• pp.959-965
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• 2014

This paper summarizes the previous research results of fundamental investigation done in SNU on the wireless power transfer. Firstly, the physical limitation of a wireless power transfer using the spherical modes is reviewed. It is found that wireless power transfer depends only on the radiation efficiency of the antennas and the distance between two antennas involved. Secondly, we review the characteristics of WPTS with different sources and compare the performance differences of WPTS according to the source type. In addition, the method for efficient WPTS is suggested when the distance between antennas is varied. Finally, by using the time domain solution of the coupled mode equation, we present an analytic formula which can be used to differentiate Inductive Coupling(IC) and Magnetic Resonance Coupling(MAC) which are often used ambiguously in wireless power transfer system.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.18 no.8
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• pp.1798-1804
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• 2014

A novel inductive resonator for the implementation of wireless power transfer using resonant inductive coupling is presented. The proposed inductive resonator is much smaller than the helix shape resonator suggested by MIT research team but operates the same resonant frequency with comparable wireless power transfer efficiency. The proposed inductive resonator is a spiral shape ($1,696cm^3$), which is 97 % smaller than the helix shape ($59,376cm^3$). The wireless power transfer efficiency is less than 9 % when compared to the helix shape resonator. With the reduce size and comparable efficiency, this novel inductive resonator can be used in practical application of wireless power transfer.

• International Journal of Railway
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• v.7 no.3
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• pp.71-79
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• 2014

Subway systems have been a proved method of public transport and are widely used in major cities around the world. However, the time and cost it takes to construct such systems are very high, as it requires underground tunnels. Cities in various countries have implemented monorail systems as public railway transport as it can be more economical and quicker compared to subway systems in terms of construction. In addition, it provides more convenience towards the public as it is not affected to traffic, and also provides an aerial view of the city. However, the overall construction cost for monorail systems is still significantly high, and as a possible solution to further reduce the overall cost, implementation of ground-level stations and wireless power transfer technology has been proposed in this paper. A concept application layout of ground-level stations and wireless power transfer systems has been discussed, using the Daegu monorail Line 3 system as a simulation base. The expected cost for monorail systems implementing ground-level stations and/or wireless power transfer technology has been estimated based on literature survey, and was compared with the current construction cost of Daegu monorail system. Based on comparison, it has shown that implementation of ground-level stations are the most economical, and can be easily implemented for either starting or expanding the monorail line. Implementation of wireless power transfer technology is also economical, but is more feasible when starting a new monorail line as it requires components which will alter the configuration of the train and infrastructure.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.53 no.3
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• pp.129-134
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• 2004

The Available Transfer Capability (ATC) is defined as the measure of the transfer capability remaining in the physical transmission network for further commercial activity above already committed uses. The ATC determination s related with Total Transfer Capability (TTC) and two reliability margins-Transmission Reliability Capability (TRM) and Capacity Benefit Margin(CBM) The TRM is the component of ATC that accounts for uncertainties and safety margins. Also the TRM is the amount of transmission capability necessary to ensure that the interconnected network is secure under a reasonable range of uncertainties in system conditions. The CBM is the translation of generator capacity reserve margin determined by the Load Serving Entities. This paper describes a method for determining the TTC and TRM to calculate the ATC in the Bulk power system (HL II). TTC and TRM are calculated using Power Transfer Distribution Factor (PTDF). PTDF is implemented to find generation quantifies without violating system security and to identify the most limiting facilities in determining the network’s TTC. Reactive power is also considered to more accurate TTC calculation. TRM is calculated by alternative cases. CBM is calculated by LOLE. This paper compares ATC and TRM using suggested PTDF with using CPF. The method is illustrated using the IEEE 24 bus RTS (MRTS) in case study.