• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.21 no.6
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• pp.562-569
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• 2011

In this study linear and nonlinear dynamic stability characteristics of a medium-size high-speed turbocharger, whose rotor is supported by two 3-lobe journal bearings, are analyzed to evaluate and identify the effects of its bearing design variables. The rotor has the rated speed of 40,500 rpm and maximum continuous speed of 45,000 rpm. At first, utilizing the linear stability analysis method, bearing designs of yielding stable or unstable LogDecs as small as possible are searched by manipulating with machined bearing clearances and preloads. As next, utilizing the nonlinear analysis method, limit cycles of the rotor responses at the rated and maximum continuous speeds are simulated to check their acceptances. Results have shown that for the turbocharger rotor-bearing system considered, the 3-lobe journal bearing design with a smaller machined clearance and a larger preload are preferred for the stable rotor responses. More importantly, since there exists a good correlation between the linear and nonlinear stability analysis results, it is concluded that firstly the linear stability analysis method may be applied to screen quickly the ranges of bearing designs for stable or least unstable solutions and then, lastly the nonlinear stability analysis method may be deployed to check an absolute motion stability in terms of the limit cycle.

• Transactions of the Korean Society of Mechanical Engineers
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• v.3 no.2
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• pp.60-67
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• 1979

Aerodynamic forces acting on a curved blade are computed theoretically taking into account the variation of wind speed over the blade to investigate the performance of a vertical axis wind rotor. It is shown that the rotor does not self start at the rated wind speed without a supplementary starting device and that most of the power output is contributed by the central portion of the rotor, and the use of spoilers for limiting the maximum rotational speed is needed for safety. It is also shown that provision of skew angle to the blade does not improve the starting characterstics and only reduces the maximum power output. The effects of geometric variables such as skew angle, blade solidity and ratio of the rotor height to diameter are also discussed.

• The Transactions of the Korean Institute of Electrical Engineers B
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• v.52 no.7
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• pp.299-306
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• 2003

Doubly-Fed Induction Generator(DFIG) is adequate to maximize the energy capture from wind energy, whereby the turbine speed can be adjusted to a speed, at which a rated tip speed ratio be kept. In this paper, a power analysis for DFIG and its characteristics of power flow in grid-connected operation, are dealt with in speed range of super- and sub-synchronous region. In a test of the machine, whereby a doubly excited circuit configuration in stator as well as rotor with back to back PWM inverter have been equipped, a constant input torque is given and in that condition, power new in stator and rotor circuit have been measured and compared with theoretical value. Furthermore, the power factor in stator and rotor circuit have been examined.

• Proceedings of the KIEE Conference
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• 1998.07a
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• pp.6-8
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• 1998

This paper deals with the maximum output power generation using the Dounly Fed Induction Generator(DFIG) in the super-synchronous speed regions, by control of both magnitude and phase of the voltage fed to the rotor. Steady-state algebraic equations of the euivalent circuit are solved using numerical analysis. For the normal operating region, in which the generator ratings are not exceeded, rotor current is less than or equal to the rated value. By selecting the permisible rated current at rotor coil, there are the optimal solution existng which covers the magnitude and phase of the injected voltage to the rotor for the given slip. This optimal solution is pointing out how the maximum output power can be carried out.

• Proceedings of the KIEE Conference
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• 1994.07a
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• pp.208-210
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• 1994

In this paper, the design sensitivity evaluation based on the 2-dimensional finite clement discretization is presented for the voltage source and eddy current problem. And it is applied to the two shape design problems of the rotor slot of 3-phase squirrel cage induction motors. The first is to increase the starting torque while keeping the rated torque fixed. The other is only to increase the torque at the rated speed while keeping the starting torque fixed. As an optimization method, the Gradient Projection method is used to control casily the torques for various speeds of rotor. One fourth of rotor is analyzed by using a semi-periodic boundary condition. Because the shape of rotor slot has much influence on the slip torque characteristic, the 10 design parameters are taken on the interface between rotor core and rotor bar. The initial shape of rotor slot is the trapezoidal typo with rounding corners.

• Progress in Superconductivity and Cryogenics
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• v.6 no.3
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• pp.33-37
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• 2004

This paper presents the construction and test results of an HTS induction motor. End rings and short bars were made of HTS tapes, To increase the efficiency and starting torque, HTS tapes can be used as the rotor bars. Because large current is induced in the rotor circuit, HTS tapes quench and high starting torque can be obtained. As the speed of rotor builds up. HTS tapes which are used as short bars become superconducting state again. After the HTS tapes recover from quench, resistance of the rotor circuit is nearly zero. In that case, power loss in rotor circuit is eliminated. Stator of the conventional induction motor was used as the stator of the HTS motor. Rated capacity of the conventional motor was 0.75 kW. Performances of the HTS induction motor were compared with those of the conventional motor with same volume and specification. Test result showed that the speeds of the HTS induction motor were the same with synchronous speed up to 2.6 Nm and 1.788 rpm at 9.7 Nm. It guarantees the high efficiency of the HTS motor. Starting torque of the HTS motor was more than twice of the conventional motor.

• 전기의세계
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• v.16 no.1
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• pp.7-13
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• 1967

There are many kinds of motors operating by rated voltage which is constant. In this paper, the characteristics of separately excited direct current motor is analyzed when its terminal voltage is varied as its load current. As for this source, direct current generator of a series field is used, and it is driven at constant speed by a primemover. The induced voltage of the generator is propotional to its load current but it saturates as its load current is large. The charateristics of motor is studied by analog computer because of the nonlinearity of generator. The results are as follows: (1) The load current and the rotor speed of motor increase as the load of motor increases. But the speed of rotor decreases for the influence of the saturation of the iron of generator field when its load current is large. (2) Decreasing the inertia of motor and increasing the inductance of the armature circuit improve the stability of motor and the region of stable state. (3) By changing the field current of the motor, the speed and the direction of rotor can be controlled in wide range.

• 제어로봇시스템학회:학술대회논문집
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• 2001.10a
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• pp.166.2-166
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• 2001

This paper is concerning a vector control of wound-rotor induction motor from the secondary side. When the wound-rotor induction motor is vector controlled from the secondary side, it has the possibility that the vector control can be accurately done because the disturbance input, that is, primary voltage and all state variables, that is, primary currents and secondary currents can be detected. We consider it is deserve research that the vector control of wound-rotor induction motor from the secondary side, because there is the merit that we can reduce the inverter capacity to on the order of half of the motor capacity when we choose twice of the synchronous speed to the rated speed, though there is the problem of the brush maintenance. In this paper, the vector control method of wound-rotor induction ...

• The Transactions of the Korean Institute of Power Electronics
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• v.27 no.5
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• pp.438-445
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• 2022

Blade efficiency decreases when the rotor speed is kept constant even though the wind speed is higher than the rated value. Therefore, a speed controller is used to regulate the rotor speed in the high-wind-speed region. In stall-blade wind turbine, the role of the speed controller is important because precise aerodynamic regulation is unavailable. In this study, an effective parameter design method of a PI speed controller is proposed to limit the speed overshoot of a type 4 wind turbine with stall blades even though wind gust occurs. The proposed method considers the efficiency characteristics of the stall blade and the mechanical inertia of the wind turbine rotor. It determines the bandwidth of the speed controller to comply with the speed limit during generator speed overshoot for the worst case of wind gust. The proposed method is verified through intensive simulations with a MATLAB/SIMULINK model and experimental results obtained using a 3 kW MG set of wind turbine simulator.

• Proceedings of the KSME Conference
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• 2001.06a
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• pp.848-853
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• 2001

A study about the shrink fits of rotor and retaining ring in generator was performed for the cases of three radial interference. The shrink-fitted retaining ring used to restrain the end turns of the winded coils in the rotor against centrifugal force requires very careful attention during design and manufacture because it has traditionally been the highest-stressed component of the generator. The contact pressures and residual stresses were obtained by the finite element analysis for each radial interference at zero, 100% rated, and 120% rated speeds, respectively. The results of analysis show that the radial interference in use needs to be increased carefully.