• 전력전자학회:학술대회논문집
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• 전력전자학회 2011년도 전력전자학술대회
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• pp.524-526
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• 2011

This paper focuses on study on PWM converter control under unbalanced network condition. Voltage unbalance in a three-phase system causes the performance deterioration by producing 120 Hz voltage ripples in the DC link and 120 Hz ripple in reactive power. To eliminate the ripples, both positive and negative sequence currents should be controlled simultaneously. In this paper four PI controllers on synchronous reference frame is implemented to control D and Q currents in both positive and negative sequence. Positive and negative sequence signal extraction is done using delay signal cancellation method. Simulation results show satisfactory performance in suppressing 120 Hz ripples.

• 한국정밀공학회지
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• 제24권11호
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• pp.91-100
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• 2007

Many manufacturing devices must execute motions as quickly as possible to achieve profitable high-volume production. Most of them have devices having flexibility and a time delay of one sampling is added to the plants when they are controlled by fast discrete controllers, which brings about non-minimum phase zeros. This paper develops a control strategy that combines feedforward and feedback control with command shaping for such devices. First, the feedback controller is designed to increase damping and eliminate steady-state error. Next, the feedforward controller is designed to speed up the transient response. Finally, an appropriate reference profile is generated using command-shaping techniques to ensure fast point-to-point motions with minimum residual vibration. The particular focus of the paper is to understand the interactions between these individual control components. The resulting control strategy is demonstrated on a model of a high-speed semiconductor manufacturing machine.

• 대한산업공학회지
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• 제27권4호
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• pp.379-383
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• 2001

The restricted shortest path problem is known to be weakly NP-hard and solvable in pseudo-polynomial time. Four fully polynomial approximation schemes (FPAS) are available in the literature, and most of these are based on pseudo-polynomial algorithms. In this paper, we propose a new FPAS that can be easily derived from a combination of a set of standard techniques. Although the complexity of the suggested algorithm is not as good as the fastest one available in the literature, it is practical in the sense that it does not rely on the bound tightening phase based on approximate binary search as in Hassin's fastest algorithm. In addition, we provide a review of standard techniques of existing works as a useful reference.

• International Journal of Aeronautical and Space Sciences
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• 제18권2호
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• pp.222-235
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• 2017

In this study, finite element modeling was used to predict the material properties of tri-axially braided textile composite. The model was made based on an experimental test specimen which was also used to compare the final results. The full interlacing of tows was geometrically modelled, from which repeating parts that make up the whole braid called unit cells were identified based on the geometric and mechanical property periodicity. In order to simulate the repeating nature of the unit cell, periodic boundary conditions were applied. For validation of the method, a reference model was analyzed for which a very good agreement was obtained. Material property calculation was done by simulating uniaxial and pure shear tests on the unit cell. The comparison of these results with that of experimental test results showed an excellent agreement. Finally, parametric study on the effect of number of plies, stacking type (symmetric/anti-symmetric) and stacking phase shift was conducted.

• 한국항행학회논문지
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• 제3권2호
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• pp.120-131
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• 1999

마그네트론을 이용하여 송신 펄스를 발생하는 레이다에서 위상을 측정하기 위해서는 송신주파수의 변화에 대해서도 안정된 중간주파수를 발생할 수 있도록 STALO(Stable Local Oscillator)의 주파수를 조정하여야 한다. 레이다 수신기의 AFC(Automatic Frequency control) 회로는 마그네트론에서 발생하는 송신주파수와 STALO의 국부발진주파수를 비교하여 일정한 중간주파수가 발생하도록 STALO 주파수를 제어한다. 본 논문에서는 안정된 중간주파수를 발생하기 위한 AFC 회로를 설계, 제작하였으며, 주파수 변화를 검출하여 비교하는 아날로그 부분과 STALO에 주파수 제어신호를 공급하는 디지털 부분을 개발하였다.

• 한국연소학회:학술대회논문집
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• 한국연소학회 2012년도 제45회 KOSCO SYMPOSIUM 초록집
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• pp.137-138
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• 2012

The two-equation soot model based on the transient laminar flamelet model is implemented for soot formation of laminar non-premixed $CH_4/Air$ flame with detailed chemical reaction mechanism and complex thermodynamic properties. The soot model represents nucleation, growth and oxidation with gas-phase chemistry. This represented unsteady flamelet soot model has been tested and compared using well verified reference calculation result obtained solving the Full Transport Equations method.

• Journal of Power Electronics
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• 제9권3호
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• pp.438-446
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• 2009

The performance of direct torque controlled (DTC) interior permanent magnet (IPM) machines is poor at low speeds due to a few reasons, namely limited accuracy of stator voltage acquisition and the presence of offset and drift components in the acquired signals. Due to factors such as forward voltage drop across switching devices in the three phase inverter and dead-time of the devices, the voltage across the machine terminals differ from the reference voltage vector used to estimate stator flux and electromagnetic torque. This can lead to instability of the IPM drive during low speed operation. Compensation schemes for forward voltage drops and dead-time are proposed and implemented in real-time control, resulting in improved performance of the space vector modulated DTC IPM drive, especially at low speeds. No additional hardware is required for these compensators.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1988년도 추계학술대회 논문집 학회본부
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• pp.53-55
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• 1988

The application of Sliding Mode Control for inproving the dynamic response of a Multi-Phase-Bipolar (MPB) Brushless DC motor based position Brushless DC motor system is presented. Sliding Mode Control gives fast dynamic response with no overshoot and zero steady state error. It has the important feature of bins highly robust. A design procedure is outlined for the Sliding Mode Controller for a MPB Brushless DC motor. Digital computer simulation of the overall position control system is carried out using a time domain model in the d-q reference frame.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 하계학술대회 논문집
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• pp.157-160
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• 2001

Three sets of ZnO ceramic devices (reference samples with Matsuoka\`s composition; added 7o MgO, A1$_2$O$_3$, SiO$_2$) have been prepared by the conventional mixed oxide route. These additives were determined by the factors of valences and ionic radiuses. DC accelerated degradation test was performed for analysis of degradation characteristics versus the various additives. The conditions of DC degradation test were 115${\pm}$2$^{\circ}C$ for 12h. Using XRD and SEM, the Phase and microstructure of samples were analyzed respectively. E-J analysis was used to determine ${\alpha}$. Frequency analysis was accomplished to understand the relationship between R$\sub$g/ and $R_{b}$ with the electric stress at the equivalent circuit.

• 대한전기학회논문지
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• 제43권6호
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• pp.936-945
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• 1994

This paper proposes a new power converter which consists of two identical 3-phase PWM modulators and a novel resonant circuit. A new control strategy is integrated to realize the bidirectional power converter without an electrolytic link capacitor. The power flow between converters is bidirectional and the regenerative braking is inherent. The source side currents maintain sinusoidal waveforms with a unity power factor. It is observed in the experiment that by balancing the active power between the source and load side, the voltage across a small ceramic link capacitor can be maintained within a small deviation from the reference. Simulation results and experimental results are presented to verify the operational principles.