• Journal of the Institute of Electronics Engineers of Korea SD
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• v.42 no.12
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• pp.19-26
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• 2005

We have studied the relationship between static mode behavior and dynamic characteristics of multiple transverse-mode VCSELs by measuring the modal L-I and I-V characteristics. Dependence of the resonance frequencies of RIN (relative intensity noise) spectra on the injection current can be understood by modal L-I characteristics and mode-coupling effects. Each transverse mode behaves as an independent diode laser with the different threshold current in large active-area VCSELs, and the multiple-step turn-on is observed when step-current input is applied. This multiple-step turn-on is a result of different turn-on delay times of the transverse modes. Since the multiple-step turn-on increases the rise-time significantly, the wide active-area VCSELs are not suitable for high-speed optical transmitters unless the input current is adjusted for single transverse-mode operation.

• Proceedings of the KIPE Conference
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• 2001.10a
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• pp.414-417
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• 2001

SRG (Switched Reluctance Generator) have many advantages such as high efficiency, low cost, high-speed capability and robustness compared with characteristics of other machines. However, the control methods that have been adopted for SRGs are complicated. This paper proposes a simple control method using PID controller that only controls turn-off angles while keeping turn-on angles of SRG constant. The linear characteristics between the generated current and the turn-off angle can be used to control the turn-off angle for load variations. Since the reference current for generation can be produced from an error between the reference and the real voltage, it can be controlled to keep the output voltage constant. The proposed control method enhances the robustness of this system and simplifies the hardware and software by using only the voltage and speed sensors. The proposed method is verified by experimental results.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.1081-1086
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• 2008

During the manufacturing process of a propeller for a large scale commercial ships, several times of turn-over process should be required. Propeller turn-over is a indispensible process but not easy because of its heavy weight and complicate shape. Recently, we developed a new type of turn-over system for a large scale propeller. The system consists of turning roller devices, sliding transfer system, clamping devices and so on. In this paper, we described the design process which includes mechanical structure design, dynamic analysis and assembly with a laser tracker.

• The Transactions of the Korean Institute of Power Electronics
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• v.22 no.2
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• pp.181-184
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• 2017

This study analyzes the turn-on and turn-off transients of a metal-oxide-semiconductor field-effect transistor (MOSFET) with high-switching frequency systems. In these systems, the voltage distortion becomes serious at the output terminal of a Vienna rectifier by the turn-off delay of the MOSFET. The current has low-order harmonics through this voltage distortion. This paper describes the transient of the turn-off that causes the voltage distortion. The algorithm for reducing the sixth harmonic using a proportional-resonance controller is proposed to improve the current distortion without complex calculation for compensation. The reduction of the current distortion by high-switching frequency is verified by experiment with the 2.5-kW prototype Vienna rectifier.

• Proceedings of the KIEE Conference
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• 1995.07c
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• pp.1205-1208
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• 1995

The optically-gated p-i-n diode switches have been fabricated with gold-compensated silicon. The turn-on and turn-off delay times and the rise and fall times were measured as a function of optical power level, bias, and pulse width. The turn-on characteristics shows a strong dependence an optical pulse power and a delay time(${\delta}{\iota}$) between two pulses, but a weak dependence on the width of optical pulse. Actually there is no turn-off delay in gold-doped p-i-n switches and the fall time is negligible.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.53 no.3
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• pp.168-174
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• 2004

On-line monitoring system(OMS) has been developed for the pumped storage generator/motor The OMS is applied to diagnosis of the PD(partial discharge) activity of stator insulation, the shorted-turn of rotor winding and the variation of the air-gap between stator and rotor. The OMS consists of DAS(data acquisition system), main server system, gateway and display PC. The DAS measures the PD, the shorted-turn and air-gap from three sensors installed on the generator/motor. The gateway controls the data which sent by DAS. The main server system saves the data, analyzes the data and conducts the diagnostic algorithm. The display PC shows the diagnostic results of partial discharge, shorted-turn and air-gap. Field tests were conducted using PDA(partial discharge analyzer). The results of the OMS and PDA measurements can be directly correlated with normalized quantity number(NQN), PD magnitude(Qm) and PD pattern.

• Journal of international Conference on Electrical Machines and Systems
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• v.2 no.1
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• pp.23-30
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• 2013

This paper proposes a parametric model for inter-turn fault detection in a fault-tolerant permanent-magnet (FTPM) machine, which can predict the effect of the short-circuit fault to various physical quantity of the machine. For different faulty operations, a new effective stator inter-turn fault detection method is proposed. Finally, simulations of vector-controlled FTPM machine drives are given to verify the feasibility of the proposed method, showing that even single-coil short-circuit fault could be exactly detected.

• Proceedings of the KIPE Conference
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• 2003.11a
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• pp.210-213
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• 2003

Short-circuited can have significant effects on a generator and its performance. One of effective method detecting inter-turn short circuits on round rotor winding is a method using sensor detecting. But the method needs duplicate design of sensor for characteristic change according to types and forms of generator. Thus rotor shorted-turn diagnosis method without sensor is needed for detecting short turn when generator is driven. Diagnosis method without sensor depend on change of electric property in generator For the reason, this paper presents characteristic analysis of shorted-turns in generator by detecting the output voltage of generator.

• Proceedings of the KIPE Conference
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• 2005.07a
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• pp.476-478
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• 2005

This paper describes a method for the detection of shorted-turn in the cylindrical synchronous generator rotor windings based on the discrete wavelet transform. Multi-resolution analysis(MRA) based on discrete wavelet transform provides a set of decomposed signals in independent frequency bands. In the proposed method, shorted-turn detection in rotor windings is based on the decomposition of the rotor currents, where wavelet coefficients of these signals have been extracted. Comparing these extracted coefficients is used for diagnosing the healthy machine from faulty machine. Experimental results show the effectiveness of the proposed method for shorted-turn detection in the cylindrical synchronous generator rotor windings.

• The Transactions of the Korean Institute of Electrical Engineers C
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• v.48 no.11
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• pp.742-747
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• 1999

On-line diagnosis system has been developed and is now applied the detection of shorted turns in the field winding of large generator. This system consists of data aquisition system and display PC. The data aquisition system detects voltage waveforms from flux probe sensor installed in the stator slot. The display PC shows theshorted-turn situation of generator rotor winding. A shorted-turn diagnosis test wasperformed on five gas turbine generators at the Seoinchon combined cycle power plant. The test was conducted using an new diagnosis system and digital oscilloscope which can identify the pole location, the slot number and the number of shorted turns within each slot. It is confirmed that results of two systems are very same in the field tests.