• Journal of Mechanical Science and Technology
• /
• v.15 no.12
• /
• pp.1816-1821
• /
• 2001

Two-dimensional blow-down type supersonic wind tunnel was designed and built to investigate the transient behavior of the startup of a supersonic flow from rest. The contour of the divergent part of the nozzle was determined by the MOC calculation. The converging part of the nozzle, upstream of fille throat was contoured to make the flow uniform at the throat. The flow characteristics of the steady supersonic condition were visualized using the high-speed schlieren photography. The Mach number was evaluated from the oblique shock wave angle on a sharp wedge with halt angle of 5 degree. The measured Mach number was 2.4 and was slightly less than the value predicted by the design calculation. The initial transient behavior of the nozzle was recorded by a high-speed digital video camera with schlieren technique. The measured transition time from standstill to a steady supersonic flow was estimated by analyzing the serial images. Typical transition time was approximately 0.1sec.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.04a
• /
• pp.869-873
• /
• 2008

Optimization method for the open loop commutation time intervals in HDD spindle start-up control is presented in this paper. A hard disk drive(HDD) uses a sensorless brushless DC motor(BLDC) for the platter rotation. Because there is no direct sensor for the rotor position, open loop commutations after sensing the rotor position at a standstill using inductive sensing method are performed to speed up the rotor up to a certain speed where the zero crossings of the back electromotive force(EMF) are measurable. Therefore successful open loop commutations are necessary for the stable start-up control of the spindle motors. Random neighborhood search(RNS) algorithm is introduced as a optimization technic in this paper. Rotor speed and its standard deviation are used as a cost function and commutation intervals obtained from the spindle motion equation are used as initial parameter values for the RNS. With the help of the proposed method optimized open loop commutation time intervals for the very low start-up current are acquired and tested. The experimental results shows that the proposed method can decrease the start-up failure rate of a HDD spindle motor.

• 제어로봇시스템학회:학술대회논문집
• /
• 1992.10b
• /
• pp.388-393
• /
• 1992

An infrared range finder using a self-mixing laser diode (SM-LD), which has been proposed and developed by the Authors, can measure not only a range of a moving target but its velocity simultaneously. In this paper, described is that the precise mode-hop pulse train can be obtained by employing a new signal processing circuit even when the backscattered light returning into the SM-LD is much more weaker. As a result, the distance to a tilted square sheet made from aluminium or white paper, which is placed 10 cm through 60 cm from the SM-LD, is measured with accuracy of a few percent even when the tilting angle is less than 75 degrees or 85 degrees, respectively. And in this paper, described is the range-image recognition of a plane object under the condition of standstill. The output laser beam is scanned by scanning two plane mirrors-equipped with each stepping motor. And we succeeded in the acquisition of the range-image of a plane object in a few tens of seconds. Furthermore, described is a feasibility study about the range-image recognition of a slowly moving plane object.

• Journal of Electrical Engineering and Technology
• /
• v.10 no.3
• /
• pp.1086-1092
• /
• 2015

The off-line and on-line partial discharge (PD) in the stator winding of three high-voltage (HV) motors (1,400 HP, 6.6 kV) is measured and analyzed in this paper. The off-line PD is measured at high values between 24,300 ~ 36,100 pC after 18 years of motor operation. Spare replacement motors were not available for testing the degree of deterioration of the stator windings in standstill status. Therefore, on-line periodic analysis was conducted to monitor the trend of PD after installing a ceramic sensor (110 pF, 6.6 kV) in the terminal box for each phase of each motor. In the stator winding of the No.1 and No.2 HV motors, which showed high magnitudes of off-line PD and low magnitudes of on-line PD, defects are expected to appear in the neutral end of the winding. On the contrary, in the stator windings of the No.3 HV motor, which exhibits high off-line and on-line PD magnitude, defects are expected to appear in the terminal end of the winding where a voltage close to the phase voltage is applied.

• Proceedings of the KIEE Conference
• /
• 2015.07a
• /
• pp.652-654
• /
• 2015

Integrated switched reluctance motor drive as an electric vehicle battery charger is presented in this paper. The SRM, which is used as the traction power in the driving mode, is used in the charge circuit to improve the power factor of charging system. The charging circuit can share the power switches of the asymmetric converter and phase windings of SRM to charge the battery, and can reduce the size and cost of the system in the plug-in system. To keep the rotor at standstill, zero torque control method is proposed. Since the inductances of the SRM windings are not same at any stop position, the charger controller controls the reference current to satisfy the total charging current with PFC and zero torque condition. A novel cubic equation method is proposed as a current reference distributor of the charging controller. Simulations are performed by MATLAB software and results satisfy the Effectiveness of proposed battery charging system.

• Journal of Information Technology Services
• /
• v.9 no.1
• /
• pp.141-156
• /
• 2010

Service industry has become the integral part of economy. And the activation of industry requires a scientific and systematic approach. As one of these kinds of efforts, IBM presented a service model which consisted of strategies, processes, technology, manpower and so on through Service Science. And IBM raised the needs of considering the main issue and methodology of service model's scientific approach. On that account, this study worked out factorial definitions and measurable items by the four components of service model presented by Service Science in order for it to be measured through studies on related literature and interviews of specialists. In order to prepare an opportunity of categorizing the conception of the service model of which character was strongly intangible and of systematically approaching to it, the investigator examined related literature and applied it QFD methodology. Through this kind of redefinition, the investigator concretely conceptualized the service model which was standstill at the level of theoretical approach so far and presented guidelines with which researchers could classify it more concretely. In addition, the investigator tried to present a systematic frame which could be applied to business by working-level officials or decision-makers. Therefore, the investigator expects that study findings will be used as references for the design or implementation of service-oriented business model.

• Journal of Power Electronics
• /
• v.11 no.4
• /
• pp.464-470
• /
• 2011

In this paper, the feasibility of applying a position sensorless control technique to hybrid electric vehicles (HEVs) is practically evaluated. The proposed position estimator has a straightforward structure with properties that combines the model and the saliency tracking-based rotor position estimation for interior permanent magnet synchronous motors (IPMSMs). The proposed method can be used in the event of sensor loss or sensor recovery to sustain continuity of operations. The developed system takes into account the estimated position transition between two distinct sensorless methods. The transition is enhanced by introducing a synchronized transition algorithm based on a single tracking observer. Extensive experimental results are presented to verify the principles and show a reliable estimation performance over the entire speed range including standstill under 150% load conditions.

• The Transactions of the Korean Institute of Power Electronics
• /
• v.16 no.6
• /
• pp.602-609
• /
• 2011

This paper proposes a simple initial rotor position estimation method to obtain a stable startup performance for back EMF-based sensorless control. The proposed estimation method is achieved at standstill by using the current response to difference between each of the stator winding inductance. This initial rotor position estimation method can be easily implemented to control algorithm without any other external devices. The proposed algorithm is also not affected by motor parameter. The validity of the proposed method is demonstrated by experimental result.

• Proceedings of the KIEE Conference
• /
• 1998.07a
• /
• pp.260-262
• /
• 1998

A new method of induction motor drive, which requires not shaft encoder, is presented. This system has both torque and speed controls that are performed by vector control. The scheme is on the basis of a rotor flux speed control, which is performed by torque producing current and rotor flux, derived from the stator voltages and currents. But, there is a problem with respect to the calculated rotor flux vector, which is an integrating operation by which the rotor induced voltage is converted into the rotor flux. The calculated rotor flux does not work so that it is unstable in initial operation, as motor speed approaches zero. For the proposed rotor flux estimator, a lag circuit is employed, to which both the motor-induced voltage and rotor flux command are imposed, and it is possible to calculate even a low frequency down to standstill. We show the validity of the proposed control method through several computer simulations.

• Journal of Power Electronics
• /
• v.5 no.3
• /
• pp.173-179
• /
• 2005

In this paper, a very low cost and robust sensing method for the rotor position of a TSRM(Toroidal Switched Reluctance Motors) is described. Position information of the rotor is essential for SRM drives. The rotor position sensor such as an opto-interrupter or high performance encoder is generally used for the estimation of rotor position. However, these discrete position sensors not only add complexity and cost to the system but also tend to reduce the reliability of the drive system. In order to solve these problems, in the proposed method, rotor position detection is achieved using voltage waveforms induced by the time varying flux linkage in the search coils, and then the appropriate phases are excited to drive the SRM. But the search coil's EMF is generated only when the motor rotates. Therefore the rotor position sensing method using squared Euclidean distance at a standstill is also examined. The simulation and experimental results are presented to verify the performance of the proposed method in this paper.