• Journal of Power Electronics
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• 제15권6호
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• pp.1601-1608
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• 2015

This paper presents a PQ control strategy for micro grid inverters with axial voltage regulators. The inverter works in the voltage-controlled mode and can help improve the terminal power quality. The inverter has two axial voltage regulators. The 1st regulator involves the output voltage amplitude and output impedance, while the 2nd regulator controls the output frequency. The inverter system is equivalent to a controllable voltage source with a controllable inner output impedance. The basic PQ control for micro grid inverters is easy to accomplish. The output active and reactive powers can be decoupled well by controlling the two axial voltages. The 1st axial voltage regulator controls the reactive power, while the 2nd regulator controls the active power. The paper analyses the axial voltage regulation mechanism, and evaluates the PQ decoupling effect mathematically. The effectiveness of the proposed control strategy is validated by simulation and experimental results.

• 한국철도학회논문집
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• 제16권5호
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• pp.372-378
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• 2013

이 논문에서는 도시철도의 최대수요전력 산출을 위한 근사모델을 제시한다. 전류 벡터 반복법을 활용하여 변전소의 최대수요전력을 계산할 경우에 기존의 방법으로는 수 많은 반복 조류계산이 필요하기 때문에 계산시간 제약으로 인해 실시간 적용이 어렵다는 문제가 있다. 본 논문에서는 모든 조건이 동일한 상태에서 전원 임피던스의 변화에 따른 변전소 최대수요 전력을 빠르게 산출하는 근사모델을 제시한다. 제시된 근사 모델에 의한 산출결과가 기존 모델과 거의 유사한 정확성을 보임을 시뮬레이션을 통해 예시한다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2011년도 제40회 동계학술대회 초록집
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• pp.213-213
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• 2011

DC arc plasmatron is powerful plasma source to apply etching and texturing processing. Even though DC arc plasmatron has many advantages, it is difficult to apply an industry due to the small applied area. To increase an effective processing area, we suggest a DC-RF hybrid plasma system. The DC-RF hybrid plasma system was designed and made. This system consists of a DC arc plasmatron, RF parts, reaction chamber, power feeder, gas control system and vacuum system. To investigate a DC-RF hybrid plasma, we used a Langmuir probe, OES (Optical emission spectroscopy), infrared (IR) light camera. For RF matching, PSIM software was used to simulate a current of an impedance coil. The results of Langmuir probe measurements, we obtain a homogeneous plasma density and electron temperature those are about $1{\times}1010$ #/cm3 and 1~4 eV. The DC-RF hybrid plasma source is applied for plasma etching experimental, and we obtain an etching rate of 10 ${\mu}m$/min. through a 90 mm of reaction chamber diameter.

• KIEE International Transaction on Systems and Control
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• 제2D권2호
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• pp.120-124
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• 2002

A new methodology is presented to diagnose faults in equipment plasma. This is accomplished by using neural networks as a pattern recognizer of radio frequency (rf) impedance match data. Using a match monitor system, the match data were collected. The monitor system consisted mainly of a multifunction board and a signal flow diagram coded by Visual Designer. Plasma anomaly was effectively represented by electrical match positions. Twenty sets of fault-symptom patterns were experimentally simulated with variations in process factors, which include rf source power, pressure, Ar, and $O_$2 flow rates. As an input to neural networks, two means and standard deviations of positions were used as well as a reflected power. Diagnostic accuracy was measured as a function of training factors, which include the number of hidden neurons, the magnitude of initial weights, and two gradients of neuron activation functions. The accuracy was the most sensitive to the number of hidden neurons. Interaction effects on the accuracy were also examined by performing a 2$^$4 full factorial experiment. The experiments were performed on multipole inductively coupled plasma equipment.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2006년도 추계학술대회 논문집 전기물성,응용부문
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• pp.196-197
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• 2006

An effective method is described for monitoring the ground impedance of intelligent building and power system. Most of grounding system of buildings are interconnected to extensive grounding network of power line, signal and control line, telecommunication line, and etc. Therefore, the residual voltages of power frequency and its harmonics may have an significant influence on the accurate measurement of ground impedance. For eliminating the influence of residual voltage, we developed a test power source for generating the 110[Hz] square wave and used digital filtering method in this research.

• Journal of Electrical Engineering and Technology
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• 제9권2호
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• pp.589-599
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• 2014

On the basis of the traditional ZSI (Z-source inverter), this paper presents a ESL-${\Gamma}$-ZSI, which uses a unique ${\Gamma}$-shaped impedance network and an extended SL network for boosting its output voltage in addition to their usual voltage-buck behavior. The inverter can increase the boost factor through adjusting shoot-through duty ratio and increasing the number of inductors. Capacitor voltage stress of ESL-${\Gamma}$-ZSI is a constant when 1>D>0, and ESL-${\Gamma}$-ZSI has small inductor current stress. The working principle of ESL-${\Gamma}$-ZSI and comparison with the classical ZSI and SL- ZSI are analyzed in detail. The power loss comparison between ESL-${\Gamma}$-ZSI and Cuk converter is analyzed detailedly. Simulation and experimental results are given to demonstrate the operation features of the inverter.

• Journal of Power Electronics
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• 제19권6호
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• pp.1467-1476
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• 2019

Grid unbalanced faults can cause core saturation of power transformer and produce lower-order harmonics. These issues increase the electrical stress of power electronic devices and can cause a tripping of an entire HVDC system. In this paper, based on the positive-sequence and negative-sequence impedance model of a VSC-HVDC system as seen from the point of common connection (PCC), the resonance problem is analyzed and the factors determining the resonant frequency are obtained. Furthermore, to suppress over-voltage and over-current during resonance, a novel method using a virtual harmonic resistor is proposed. The virtual harmonic resistor emulates the role of a resistor connected in series with the commutating inductor without influencing the active and reactive power control. Simulation results in PSCAD/EMTDC show that the proposed control strategy can suppress resonant over-voltage and over-current. In addition, it can be seen that the proposed strategy improves the safety of the VSC-HVDC system under unbalanced faults.

• Journal of Power Electronics
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• 제18권4호
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• pp.1190-1200
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• 2018

A current sourced bi-directional wireless power transfer (WPT) system is proposed to solve the problems that exist in the bi-directional WPT for vehicle-to-grid (V2G) systems. These problems include the fact that these systems are not safe enough, the output power is limited and the control methods are complicated. Firstly, the proposed system adopts two different compensation and control methods on both the primary and secondary sides. Secondly, based on an AC impedance analysis, the working principle is analyzed and the parameter configuration method with frequency stability is given. In order to output a constant voltage, a bi-directional DC/DC circuit and a controllable rectifier bridge are adopted, which are based on the "constant primary current, constant secondary voltage" control strategy. Finally, the effectiveness and feasibility of the proposed methods are verified by experimental results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1989년도 하계종합학술대회 논문집
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• pp.567-570
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• 1989

A constant V/F control system of voltage contrlled PWM inverter has a unstable operation of the low- speed and the light-load. In this paper, the authors propose stability control with idealized operation of induction motor by the neglect of primary leakage inductance and resistance. Also ldealized operation system is adopted voltage error, feed back impedance circuit, and increasing resistance from dead time of switching is compensated by the soft ware with u-processors. The proposed simulation of the idealized control method is proved at the low-speed operation for three phase induction motor.

• 대한의용생체공학회:의공학회지
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• 제27권1호
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• pp.30-37
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• 2006

Injecting currents into an electrically conducting subject, we may measure the induced magnetic flux density distributions using an MRI scanner. The measured data are utilized to reconstruct cross-sectional images of internal conductivity and current density distributions in Magnetic Resonance Electrical Impedance Tomography (MREIT). Injection currents are usually provided in a form of mono-polar or bi-polar pulses synchronized with an MR pulse sequence. Given an MRI scanner performing the MR phase imaging to extract the induced magnetic flux density data, the current source becomes one of the key parts determining the signal-to-noise ratio (SNR) of the measured data. Since this SNR is crucial in determining the quality of reconstructed MREIT images, special care must be given in the design and implementation of the current source. This paper describes a current source design for MREIT with features including interleaved current injection, arbitrary current waveform, electrode switching to discharge any stored charge from previous current injections, optical isolation from an MR spectrometer and PC, precise current injection timing control synchronized with any MR pulse sequence, and versatile PC control program. The performance of the current source was verified using a 3T MRI scanner and saline phantoms.