• The Transactions of The Korean Institute of Electrical Engineers
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• v.62 no.11
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• pp.1621-1627
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• 2013

This paper compares power losses between voltage controlled before and after using power conversion device in AC feeding system. For this purpose we present voltage control procedures and criteria and model high speed line and train using PSCAD/EMTDC to compare power losses in various feeding condition. Power losses of the simulation result in power control before and after in single point feeding system was reduced maximum 0.37 MW(23.8 %) and average 0.23 MW(20.5 %) when one vehicle load operates maximum load condition. When three vehicles operate maximum load condition in one feeder section, power losses after voltage control was reduced 1.03 MW(49.5%) compared to before voltage control. And, power loss of parallel feeding system is reduced the average 0.08 MW(7.2 %) compared to the single feeding system. In conclusion, adaptive voltage control method using power conversion device can reduce power losses compared with existing method.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2000.02a
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• pp.58-59
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• 2000

The influence of voltage lead and tape arrangements on self-field losses was investigated by using a 1.5m long Bi-2223 tape. Experimental results show that the measured losses are strongly dependent on voltage lead configurations but not contact positions. The losses are independent on frequencies below critical current of the tape. It menas that the self-field losses are purely hysteretic.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.60 no.1
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• pp.71-77
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• 2011

An analysis, which is focused on electrical losses of an electrical propulsion system with High voltage DC/DC Converter (HDC) for a hybrid and an electric vehicle, is presented. From the analysis, it can be known that the electrical losses are closely related to the dc link voltage of the HDC, and there is an optimal dc link voltage which minimizes the losses. In this paper, the method to decide the optimal dc link voltage is proposed and the comparison on the losses by the control methods of the dc link voltage, during a driving cycle, is performed and the result is also presented.

• The Transactions of the Korean Institute of Electrical Engineers P
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• v.66 no.4
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• pp.219-223
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• 2017

In this paper, we calculated the losses in the high voltage lines of power distribution system. The losses caused by high voltage lines are calculated using maximum current, resistance, loss factor, and dispersion loss factor. The accurate extraction of these factors are very important to calculate the losses exactly. Thus, the maximum loads are subdivided to regions and calculated monthly for more accurate maximum current calculation. Also, the composite resistance is calculated according to the ratio of the used wire types. In order to calculate the loss factor, the load factors according to the characteristics of each region were calculated. Finally, the losses of the distribution system is calculated by adding the losses by the transformers and the low voltage lines.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• v.5B no.4
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• pp.299-305
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• 2005

The work described in this paper is to investigate the additional iron losses and consequent temperatures in core ends of a turbo-generator wound with high voltage cables. Electromagnetic calculations are made with 3D FE models, which include the lamination material with anisotropic properties both in magnetic permeability and electric conductivity. The models also include the geometry of the stator teeth and eventually the axial steps designated to reduce the core end losses. The 3D model of the rotor consists of field windings with straight in-slot parts and end windings. The thermal models are simplified into two dimensions and include the heat sources dumped from the 3D electromagnetic solutions. The influences of power factor on additional iron losses are studied for this cable wound machine and conventional machines. The calculation results show that the additional iron losses can be reduced to about $15\%$ by introducing some small steps around the airgap corner of core ends.

• Journal of Power Electronics
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• v.17 no.6
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• pp.1490-1499
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• 2017

The modular multilevel converter (MMC) is generally considered to be a promising topology for medium-voltage and high-voltage applications. However, in order to apply it to high-power applications, a huge number of switching devices is essential. The numerous switching devices lead to considerable switching losses, high cost and a larger heat sink for each of the switching device. In order to reduce the switching losses of a MMC, this paper analyzes the performance of the conventional discontinuous pulse-width modulation (DPWM) method and its efficiency. In addition, it proposes a modified novel DPWM method for advanced switching losses reduction. The novel DPWM scheme includes an additional rotation method for voltage-balancing and power distribution among sub modules (SMs). Simulation and experimental results verify the effectiveness and performance of the proposed modulation method in terms of its switching losses reduction capability.

• Progress in Superconductivity and Cryogenics
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• v.3 no.2
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• pp.21-26
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• 2001

Superconducting synchronous generators and motors are designed based on 2 dimensional electro-magnetic approach. In the case of generator, if the machine output rating and terminal voltage are decided the armature rating current will be decided automatically according to its power factor. However, in the case of motor, if the output rating is given with [hp] or [kw] units, the armature terminal voltage and current are not decided directly because the machines armature input power and mechanical output are different by way of losses. So in order to calculate the armature current more accurately. the machine losses must be included in the design procedure. In this paper the machine loss of superconducting motor are analyzed and used for decision of the armature input power and current. Moreover, the differences of voltage equations between superconducting synchronous generator and motor are considered.

• Proceedings of the KIEE Conference
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• 1998.11a
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• pp.223-225
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• 1998

This paper presents a new approach for power flow calculation, which minimizes the transmission losses in power systems with the control of voltage magnitudes on P-V nodes. In this approach, the transmission losses are re-distributed to each P-V node, at each iteration, to reduce the effect of slack. The steepest descent method is adopted, in this study, to minimize the transmission losses augmented with penalty functions to account for voltage constraints. IEEE 14 and 30 buses test systems were used for the performance demonstration of the proposed method in this paper. The simulation results showed that the proposed method can reduce transmission losses and improve voltage profiles of power systems.

• Proceedings of the KIEE Conference
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• 1998.07f
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• pp.2148-2150
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• 1998

This paper proposes a constant frequency controlled zero voltage switching method that can reduce switching losses caused by emf on inductance in DC motor. The zero voltage switching method is used more than a zero current switching method because of reducing switching losses by capacitance of depletion region of MOSFET. To simplify the controller circuit, we propose constant frequency controlled zero voltage switching method in the paper. The control method is more stable than a variable frequency control method because it can optimize bandwidth of a closed-loop and reactances. Therefore, we construct a constant frequency controlled zero voltage switching converter and improve zero switching losses in high switching frequency. In the process, we can control low-losses in full range on variable voltage and load. We simulate the proposed converter with P-SPICE and compare results obtained through the experiment.

• Journal of Power Electronics
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• v.14 no.3
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• pp.531-540
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• 2014

A novel carrier-based PWM (CBPWM) strategy of a three-level NPC converter is proposed in this paper. The novel strategy can eliminate the low-frequency neutral point (NP) voltage oscillation under the entire modulation index and full power factor. The basic principle of the novel strategy is introduced. The internal modulation wave relationship between the novel CBPWM strategy and traditional SPWM strategy is also studied. All 64 modulation wave solutions of the CBPWM strategy are derived. Furthermore, the proposed CBPWM strategy is compared with traditional SPWM strategy regarding the output phase voltage THD characteristics, DC voltage utilization ratio, and device switching losses. Comparison results show that the proposed strategy does not cause NP voltage oscillation. As a result, no low-frequency harmonics occur on output line-to-line voltage and phase current. The novel strategy also has higher DC voltage utilization ratio (15.47% higher than that of SPWM strategy), whereas it causes larger device switching losses (4/3 times of SPWM strategy). The effectiveness of the proposed modulation strategy is verified by simulation and experiment results.