• The Transactions of the Korean Institute of Power Electronics
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• v.17 no.4
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• pp.337-344
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• 2012

A matrix converter is used for converting AC/AC power directly. In order to generate sinusoidal input/output waveform in matrix converter, it uses nine bidirectional switches and PWM modulation. This paper presents an analytical averaged loss model of matrix converter with DDPWM(direct duty ratio PWM) and proposes a new switching method for reducing switching losses. A Mathematical loss models with average magnitude of voltage/current are classed as conduction and switching loss. The proposed switching pattern is improved with existing DDPWM. To prove improved efficiency with proposed DDPWM, this paper compares losses between suggested switching pattern and conventional switching pattern using mathematical and simulation method. Each loss types are influenced by environmental factors such as temperature, switching frequency, output current and modulation method.

• Journal of Magnetics
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• v.1 no.2
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• pp.90-93
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• 1996

For the design of high efficiency electric machines, analysis of higher harmonic frequency components of the magnetic induction is necessary. We have measured ac magnetic properties of non-oriented silicon steel under harmonic frequencies ranging from $3^rd$ (180 Hz) to $9^th$(540 Hz) and harmonic amplitude components from 10% to 50% of the total amplitude ($B_max$=1.5T). From the experiment, it is found that, if the magnetic induction waveform has above $9^th$ harmonic frequency components of the magnetic induction, the core losses only depended on the harmonic amplitude component, but if harmonic frequency becomes lower than 9th harmonic frequency, the core losses depend on the phase angle and the harmonic amplitude, and phase angle should be considered in the design of electric machine.

• Progress in Superconductivity and Cryogenics
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• v.13 no.3
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• pp.10-13
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• 2011

The power demand is steadily increasing due to rapidly develop of industrial field. The ratio of prospected increment of power consumption is over 2.2 % per year from 2007 to 2020 year. The superconducting fault current limiters(SFCLs) should be suggested to be one of promising machines to protect power grid. Four basis tests such as resistivity, short-circuit tests, ac losses and recovery time were investigated according to various reached maximum temperature, operating temperature. This paper deals with investigation of the various commercial high temperature superconductor for applying resistive type SFCLs.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.630-635
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• 1998

This paper establishes in a new unified manner new mathematical models with core(iron) loss factor for two kinds of AC motors, induction and synchronous motors which are supposed to generate torque precisely or/and efficiently under vector controls. Our new models consist of three basic equations consistent with the others such as differential equation describing electromagnetic dynamics, torque equation describing torque generating mechanism, energy transmission equation describing how injected energy is wasted, saved or transmitted where all vector signals are defined in general frame of arbitrary instant angular velocity. It is clearly shown in our models that equivalent core-loss resistance can express appropriately and separately both eddy-current and hysteresis losses rather than mere vague loss. Proposed model of induction motor is the most compact in sense of the number of employed interior states and parameters. This compact model can also represent eddy-current and hysteresis losses of rotor as well as stator. For synchronous motor, saliency is taken into consideration. As well known model for cylindrical motor can be obtained directly from salient one as its special case.

• Proceedings of the Korea Institute of Applied Superconductivity and Cryogenics Conference
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• 2003.02a
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• pp.254-256
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• 2003

AC loss is one of the important superconducting power machine that we have to consider deeply using the stack wires with the HTS. AC magnetic field is occurred around the wires when the electric current is conducted to the stack wires. It also brings electric field to the wires and occurs self field loss, whose quantity is appeared differently by distance of the stack wires. In this paper, transport current losses of a stack short sample of HTS were compared with Norris equation and measured value.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1999.05a
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• pp.73-76
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• 1999

We have fabricated and tested a Bi-based high temperature superconducting current lead system. Ag sheathed Bi-2223 mono-filament tapes of $I_c=8.4$ A at 77 K under self-field condition were fabricated using powder-in-tube(P1T) method. Multi-layer current leads can be made by stacking of Ag sheathed Bi-2223 mono-filament wires. The critical current of this 10-layer current lead is about 68 A. The contact resistance across the copper-current lead interface has been studied using current-voltage characteristics. At temperature below critical temperature the resistive contribution of the interface to the total contact resistance dominates. We have measured AC transport losses in a current lead at 77 K, 60 Hz by a transport method.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.13 no.7
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• pp.630-635
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• 2000

Superconducting power cable is one of the most promising energy application of high-T$\sub$2/ superconductor(HTS). Thus we investigated previously the electrical and mechanical characteristics on Bi-2223 Ag sheathed tape. And a prototype HTS cable have been designed constructed and tested. In case of 19-filament type transport losses agree with the results of norris theory(strip). The critical current of HTS cable(1, 19-filament) in LN$_2$was 116[A], 240[A] and degradation coefficient(k) was 0.71, 0.73 respectively. In case of 19-filament cable critical current was decreased because of mechanical strain at pitch. And AC loss of HTS cable(19-filament) was 0.7 [W/m] in 240[A] loading

• The Transactions of The Korean Institute of Electrical Engineers
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• v.61 no.1
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• pp.16-21
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• 2012

The growth in IT industry has brought a corresponding rise in the number of connected digital devices in the distribution network. These digital loads lead to AC to DC conversion losses in order to supply power to them. The more the renewable energies and plug-in electrical vehicles penetrated our lives, the more the electrical losses are caused by AC to DC conversion process. Hence, this paper suggests the methodology for evaluating the amount of power supplied according to the ratio of DC power supply and performs an economic analysis of DC distribution system considering grid parity. In here, the cost of carbon emission reduced by renewable energy is also concerned.

• Journal of Power Electronics
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• v.13 no.2
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• pp.197-205
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• 2013

In energy injection resonant AC-AC converters, due to the low frequency effect of the AC input envelope and the low energy injection losses requirement, the constant and steady control of the high frequency AC output envelope is still a problem that has not been solved very well. With the aid of system modeling, this paper analyzes the mechanism of the envelope pit on the resonant AC current. The computing methods for the critical damping point, the falling time and the bottom value of the envelope pit are presented as well. Furthermore, this paper concludes the stability precondition of the system AC output. Accordingly, an optimal control method for the AC output envelope is put forward based on the envelope prediction model. This control method can predict system responses dynamically under different series of control decisions. In addition, this control method can select best series of control decisions to make the AC output envelope stable and constant. Simulation and experimental results for a contactless power transfer system verify the control method.

• Korean Journal of Food Science and Technology
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• v.34 no.4
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• pp.725-731
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• 2002

Hypoglycemic effects of $H_2O$ fraction of Alisma canaliculatum (Ac) with chromium (Cr) in streptozotocin (STZ)-induced diabetic rats were investigated. Sprague-Dawley rats were divided into five groups: normal, diabetic-control, and three diabetic experimental groups. Diabetes mellitus was induced by injection of STZ (45 mg/kg) into tail vein, and $H_2O$ fraction of Ac and Cr were administrated orally to experimental rats for 14 days: Ac group (1,000 mg/kg), Cr-Ac group (Ac 1,000 mg/kg & Cr 100 mg/kg), and Cr group (100 mg/kg). Body weight losses were observed in all groups except the normal group, while the losses in experimental groups were significantly less than in diabetic-control group. The plasma glucose levels were significantly lower in Cr, Ac-Cr, and Ac groups compared to STZ-control group. Plasma cholesterol and TG levels of Ac-Cr group were significantly lower than those of diabetic-control group. Plasma HDL-cholesterol levels of three experimental groups were not significant compared to diabetic-control group, while the level of Cr group decreased more than diabetic-control group. The results suggest that there was no synergistic effect in the treatment of $H_2O$ fraction of Ac in combination with Cr, an indication that $H_2O$ fraction of Ac with Cr might possess some hypoglycemic and hypotriglyceridemic properties in STZ-induced diabetic rats.