• The Journal of Korean Institute of Communications and Information Sciences
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• v.37A no.10
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• pp.895-902
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• 2012

In this paper, we propose a novel equalizer to compensate for the group delay including AM/PM nonlinear distortion characteristics by the nonlinear power amplifier (PA). The group delay characteristic is a nonlinear non-constant time delay that appears differently depending on each frequency component. The phase distortion by AM/PM characteristics arising from the power amplifier is a major factor to increase group delay. By the group delay distortion, the signal in the constellation expands and is rotated. Considering the problem mentioned above, the nonlinear time delay that appears differently depending on each frequency component is classified as a static group delay and AM/PM characteristic of PA, the different phase transitions depending on the size of input signal as a dynamic group delay. Static group delay estimates and compensate for phase distortions in the frequency domain with type-based method and dynamic group delay compensates for phase rotation in the time domain. We confirmed that the group delay compensation techniques were enough to compensate the group delay characteristics including AM/PM characteristics of the power amplifier.

• Nuclear Engineering and Technology
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• v.36 no.4
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• pp.357-363
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• 2004

A prototype long pulse ion source was developed, and the beam extraction experiments of the ion source were carried out at the Neutral Beam Test Stand (NBTS) of the Korea Superconducting Tokamak Advanced Research (KSTAR). The ion source consists of a magnetic bucket plasma generator, with multi-pole cusp fields, and a set of tetrode accelerators with circular apertures. Design requirements for the ion source were a 120kV/65A deuterium beam and a 300 s pulse length. Arc discharges of the plasma generator were controlled by using the emission-limited mode, in turn controlled by the applied heating voltage of the cathode filaments. Stable and efficient arc plasmas with a maximum arc power of 100 kW were produced using the constant power mode operation of an arc power supply. A maximum ion density of $8.3{\times}10^{11}\;cm^{-3}$ was obtained by using electrostatic probes, and an optimum arc efficiency of 0.46 A/kW was estimated. The accelerating and decelerating voltages were applied repeatedly, using the re-triggering mode operation of the high voltage switches during a beam pulse, when beam disruptions occurred. The decelerating voltage was always applied prior to the accelerating voltage, to suppress effectively the back-streaming electrons produced at the time of an initial beam formation, by the pre-programmed fast-switch control system. A maximum beam power of 0.9 MW (i.e. $70\;kV{\times}12.5\;A$) with hydrogen was measured for a pulse duration of 0.8 s. Optimum beam perveance, deduced from the ratio of the gradient grid current to the total beam current, was $0.7\;{\mu}perv$. Stable beams for a long pulse duration of $5{\sim}10\;s$ were tested at low accelerating voltages.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.29 no.1 s.232
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• pp.110-115
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• 2005

A novel technique for fine particle beam focusing under the atmospheric pressure is introduced using a radiation pressure assisted aerodynamic lens. To introduce the radiation pressure in the aerodynamic focusing system, a 25m plano-convex lens having 2.5mm hole at its center is used as an orifice. The particle beam width is measured for various laser power, particle size, and flow velocity. In addition, the effect of the laser characteristics on the beam focusing is evaluated comparing an optical tweezers type and pure gradient force type. For the pure aerodynamic focusing system, the particle beam width was decreased as increasing particle size and Reynolds number. Using the optical tweezers type, the particle beam width becomes smaller than that of the pure aerodynamic focusing system about $16\%,\;11.4\%\;and\;9.6\%$ for PSL particle size of $2.5{\mu}m,\;1.0{\mu}m,\;and\;0.5{\mu}m$, respectively. Particle beam width was minimized around the laser power of 0.2W. However, as increasing the laser power higher than 0.4W, the particle beam width was increased a little and it approached almost a constant value which is still smaller than that of the pure aerodynamic focusing system. For pure gradient force type, the reduction of the particle beam width was smaller than optical tweezers type but proportional to laser power. The radiation pressure effect on the particle beam width is intensified as Reynolds number decreases or particle size increases relatively.

• Journal of international Conference on Electrical Machines and Systems
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• v.1 no.3
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• pp.330-335
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• 2012

Brushless doubly-fed machine (BDFM) doesn't use brush and slip ring, and has advantages such as high system reliability, small capacity of its frequency converter, low system cost, adjustable power factor and speed, etc. At the same time, it has good applicable potentials on the variable frequency motors and the variable speed constant frequency generators. However, due to the complicacy and particularity of BDFM in the structure and operating mechanism, the effect of magnetic field modulation directly influences the operating efficiency of BDFM. To study the effect of different cage rotor structures on the magnetic field modulation of BDFM, the rotor magnetomotive force (MMF) of BDFM with cage rotor is studied by the analytical method. The components and features of rotor harmonic MMFs are discussed. At the same time, the method to weaken the higher harmonics is analyzed by the theoretic formulae. Furthermore, the magnetic field modulation mechanism is expounded on in detail and the relationship between the magnetic field modulation effect and the operating efficiency of BDFM is established. And then, a new method for estimating the magnetic field modulation effect is proposed. At last, the magnetic field modulation effects of four BDFM prototypes with different cage rotor structures are compared by the MMF analysis and the efficiency data of electromagnetic design. The results verify the effectiveness of the new method for estimating the magnetic field modulation effect of BDFM with cage rotor.

• Proceedings of the KIEE Conference
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• 1998.07c
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• pp.1166-1169
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• 1998

The Load characteristic of electric railway requires the power demand of the high capacity which amplitude is spacial-temporally fluctuated due to frequent starting and stopping with large tractive force. The conventional electric railway mainly consists of the resistance controlled and the thyristor controlled locomotives, are compensated for their bad characteristics of the power factor$(70\sim80%)$ with installation of another capacitor improving power factor at the substation. Since 1994, VVVF train car with good characteristics of power factor(100%) have been introduced and operated in Kwa-Chon Line. From the present technical tendency, it is judged that introduction of the locomotive with various controlled methods is necessary. The protective equipments installed at the substation are complicated and various aspects to detect faults and reduce their extension, so the universal countermeasures are required. Specially in the case of the fault occurrence it is difficult to calculate the fault location because of the change in the contactline constant according to modifying the characteristics of the contactline (the dualized catenary wire and extension, etc), so much time is required for the detection of fault location. In BT-fed method distance-relays and fault-locators are not installed, we have so many difficulties in the quick accident recovery.

• The Journal of Engineering Geology
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• v.18 no.2
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• pp.207-214
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• 2008

We conducted uniaxial consolidation tests in mudstone samples with different clay content, in order to investigate time-dependent deformation and its characteristics. A significant amount of time-dependent strain was observed at a constant stress level immediately after a jump of stress was applied. For a given mudstone, the amount of time-dependent deformation was nearly proportional to the increment of stress, suggesting a linear viscous rheology. The amount of time-dependent strain increases with clay content, implying that clay plays an important role in creep of the unconsolidated mudstone. A power-law model was suitably applied to our results, suggesting that a short-term prediction of time-dependent deformation of the mudstone is tentatively feasible.

• Proceedings of the KIEE Conference
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• 2007.07a
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• pp.226-227
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• 2007

The purpose of this study for photovoltaic (PV) generation system is to keep the output power of photovoltaic cells maximized under any weather conditions. In a conventional MPPT (Maximum Power Point Tracking) control method, both voltage and current coming out from PV array have to be fedback. Thus, the system has a complex structure, and may fail to track MPP of PV array when unexpected weather conditions happen. This paper proposes a novel PV Output Senseless (POS) control method to solve the mentioned problem. The main advantage of this method is that the current flowing into load is the only one considerable factor. In case of a huge PV generation system, it can be operated much more safely than the conventional system. To verify this theory, results that compare and analyze the simulated data with experimental data under real weather condition of the manufactured PV generation system are shown in this paper. Authors vividly states that this theory uses constant resistors and variable resistors of DC-DC converter in PV system. Authors emphasize that it is a very useful method to maximize power from PV cells to load with only the feedback of load current. Authors also emphasize that this theory is applicable in case of the PCS in PV power generation system.

• The Transactions of the Korean Institute of Power Electronics
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• v.12 no.4
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• pp.291-299
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• 2007

To operate a permanent magnet synchronous motor (PMSM) at a maximum torque per ampere (MTPA) operation point, the exact values of machine parameters such as inductances and back-EMF constant, which are sensitive to motor phase currents and temperature respectively, should be blown. An adaptive estimation method for on-line estimation of the machine parameters is not suitable for practical applications since it has difficulties in estimating exact values and requires complex mathematical calculations. The purpose of this paper is to present a simple MTPA operation point tracking control strategy for vector controlled PMSM drives with slow dynamic loads. The proposed method searches MTPA operation points by modulating current phase angle and observing the variation in command power. The current angle modulation strategy is designed to sense the effect of load variations in the command power. Therefore, the proposed method can track the MTPA operation points of the PMSM regardless of load variations. Computer simulation and experimental study is also presented to show the effectiveness of the proposed method.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2007.11a
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• pp.261-261
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• 2007

Wearable and ubiquitous micro systems will be greatly growing and their related devices should be self-powered in order to avoid the replacement of finite power sources, for example, by scavenging energy from the environment. With ever reducing power requirements of both analog and digital circuits, power scavenging approaches are becoming increasingly realistic. One approach is to drive an electromechanical converter from ambient motion or vibration. Vibration-driven generators based on electromagnetic, electrostatic and piezoelectric technologies have been demonstrated. Among various generator types proposed so far, piezoelectric generator possesses considerable potential in micro system. To overcome low mechanical-to- electric energy conversion, the piezoelectric device should activate in resonance mode in response to external vibration. Normally, the external vibration excretes at low frequency ranging 0.1 to 200 Hz, whereas the resonant frequencies of the devices are fixed as constant. Therefore, keeping their resonant mode in varying external vibration can be one of important points in enhancing the conversion efficiency. We investigated the possibility of use of multi-bender type piezoelectric devices. To match the external vibration frequency with the device resonant frequency, the various devices with different resonant frequency were chosen. Under an external vibration acceleration of 0.1G at 120 Hz, the device exhibited a peak-to-peak voltage of 2.8 V and a power of 0.5 mw in resonance mode.

• Proceedings of the Korea Water Resources Association Conference
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• 2012.05a
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• pp.11-17
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• 2012

The Waikato River is New Zealand's longest River, though relatively small on international scales. It drains the central North Island and has New Zealand's largest lake (Lake Taupo) at its headwaters. The upper reaches have sustained flows fed by large aquifers which are recharged by rainfall events providing relatively constant river flows, whereas the lower reaches respond more directly to rainfall events having more peaky flows after rainfall and extreme low flows during dry periods. Consumptive allocation from the river is relatively low with only about 3% of the mean annual flow being allocated. However, more than seven times the river's flow is allocated for non-consumptive purposes before discharging to the Tasman Sea. The majority of this non-consumptive allocation is for hydro power generation and as cooling water at both thermal and geothermal power stations which produce up to 25% of New Zealand's electricity. The upper half of the river has been heavily modified with the construction of eight dams for power generation. This has resulted in a succession of cascading dams replacing the previously uncontrolled river. The Waikato River also provides drinking water for Auckland City (NZ's largest city) and Hamilton City (NZ's 4th largest city). In recent years there has also been considerable growth in water requirements for pasture irrigation to support the intensification of dairy farming in the catchment. Operators of the power stations are concerned that any further consumptive allocation will further reduce their ability to generate electricity. The Waikato Regional Council, who is charged with managing the river and allocation of water, has recently set new rules for managing the conflicting allocation demands on the Waikato River. This has resulted in an end to further allocation of water where it results in a loss of water for electricity generation from renewable resources (fresh water and geothermal water). The exception to this is the prioritisation of water for municipal supplies ahead of other consumptive uses such as industries and irrigators.