• Title/Summary/Keyword: Voltage

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Improvement of PLL Method for Voltage Control of Dynamic Voltage Restorer (동적전압보상기의 전압제어를 위한 PLL 방식의 개선)

  • Kim, Byong-Seob;Choi, Jong-Woo
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.58 no.5
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    • pp.936-943
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    • 2009
  • Dynamic voltage restorer(DVR) is now more preferable enhancement than other power quality enhancement in industry to reduce the impact of voltage faults, especially voltage sags to sensitive loads. The main controllers for DVR consists of PLL(phase locked loop), compensation voltage calculator and voltage compensator. PLL detects the voltage faults and phase. Compensation voltage calculator calculates the reference voltage from the source voltage and phase. With calculated compensation voltage from PLL, voltage compensator restores the source voltage. If PLL detect ideal phase, compensation voltage calculator calculates ideal compensation voltage. Therefore, PLL for DVR is very important. This paper proposes the new method of PLL in DVR. First, the power circuit of DVR system is analyzed in order to compensate the voltage sags. Based on the analysis, new PLL for improving transient response of DVR is proposed. The proposed method uses band rejection filter(BRF) at q-axis in synchronous flame. In order to calculate compensation voltage in commercial instruments, the PQR theory is used. Proposed PLL method is demonstrated through simulation using Matlab-Simulink and experiment, and by checking load voltage, confirms operation of the DVR

The Study on Detecting Scheme of Voltage Sag using the Two Difference Voltage (이중 차 전압을 이용한 전압 새그 검출 기법에 관한 연구)

  • Lee, Woo-Cheol
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.28 no.12
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    • pp.65-73
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    • 2014
  • In this paper, the detection scheme of the voltage variation using a two difference voltage is proposed. The conventional sag detector is from a single-phase digital phase-locked loop (DPLL) that is based on a d-q transformation using an all-pass filter (APF). The APF generates a virtual q-axis voltage component with $90^{\circ}$ phase delay but the APF cannot generate the virtual q-axis voltage depending on the phase of the grid voltage. To overcome the problem, q-axis voltage component is generated from difference between the current and previous value of d-axis voltage component in the stationary reference frame. However, the difference voltage around the zero crossing is not enough to detect the voltage sag. Therefore, the new detection scheme using the two difference voltage which can detect the sag around the zero crossing voltage is proposed.

Output Voltage Control of Z-Source Inverter by the Detection of the Input DC Voltage and Z-Network Capacitor Voltage (입력 직류 전압과 Z-네트워크 커패시터 전압 검출에 의한 Z-소스 인버터의 출력 전압 제어)

  • Kim, Se-Jin;Jung, Young-Gook;Lim, Young-Cheol;Choi, Joon-Ho
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.60 no.8
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    • pp.1515-1522
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    • 2011
  • This paper proposes the algorithm for the output AC voltage control of Z-source inverter by the detection of the input DC voltage and Z-network capacitor voltage. The actual modulation index of the proposed method is detected by the capacitor voltage in Z-network and input DC voltage of three-phase Z-source inverter. Control modulation index for the output voltage control is calculated by the detected actual modulation index and reference modulation index. And, calculated control modulation index is applied to the modified space vector modulation (SVM) for control the output voltage of Z-source inverter. To verify the validity of the proposed method, PSIM simulation was achieved and a DSP controlled 1[kW] three-phase Z-source inverter was producted. The simulation and experiment were performed under the condition that the load was changed in case of the constant input DC voltage and the input DC voltage was changed in case of the load was constant. As a result, we could know that the output phase voltage of Z-source inverter followed to the reference voltage 70[VRMS] despite the load or the input DC voltage were suddenly changed.

A Dynamic Simulation of Voltage Instability Using EMTP (EMTP를 이용한 전압 불안정 현상의 동적 시뮬레이션)

  • 허정용;김철환
    • The Transactions of the Korean Institute of Electrical Engineers A
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    • v.52 no.6
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    • pp.295-300
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    • 2003
  • Voltage instability has been studied for some decade now. But, There is not generally accepted definition of voltage instability because of the complex phenomenon and the variety of ways in which it can manifest itself. Both IEEE and CIGRE have the respective definitions. The areas of voltage instability research are the analysis, simulation and countermeasure of voltage instability. It needs to model the components of the power system to simulate the voltage instability and voltage collapse. At the beginning, the static simulation was used. This method provides the voltage stability indices and it requires less CPU resource and gives much insight into the voltage and power problem. However, it is less accurate than the dynamic simulation peformed in the time domain simulation. So, when it appears difficult to secure the voltage stability margin in a static stability, it is necessary to perform the dynamic simulation. To perform time-domain simulation, we have to model the dynamic component of the power system like a generator and a load. The dynamic simulation provides the accurate result of the voltage instability. But, it is not able to provide the sensitivity information or the degree of stability and it is time consuming and it needs much CPU resource. In this Paper, we perform a dynamic simulation of voltage instability and voltage collapse using EMTP MODELS. The exponential load model is designed with MODEIS and this load model is connected with test power system. The result shows the process of voltage change in time domain when the voltage instability or voltage collapse occurs.

A DTC-PWM Control Scheme of PMSM using an Approximated Voltage Function of Voltage Vector (전압벡터의 근사 전압함수를 이용한 PMSM의 DTC-PWM 제어방식)

  • Kwak, YunChang;Lee, Dong-Hee
    • The Transactions of the Korean Institute of Power Electronics
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    • v.20 no.5
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    • pp.421-428
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    • 2015
  • An advanced direct torque control (DTC) with pulse width modulation (PWM) method is presented in this paper. The duty ratio calculation of the selected voltage vector is based on the voltage functions of the selected voltage vector according to the sector angle. The proposed DTC uses a conventional DTC scheme with six sector divisions and switching rules. However, the winding voltages are supplied by the PWM approach. Furthermore, the duty ratio of the switching voltage vector is determined by the flux, torque error, and motor speed. The base voltage that shall determine the duty ratio can be calculated by approximate voltage functions according to the voltage angle. For the calculation of base voltages, second-order quadratic functions are used to express the output voltage of the selected voltage vector according to voltage angle. The coefficients for the second-order quadratic functions are selected by the voltage vector, which is determined by the switching rules of the DTC. In addition, the voltage functions are calculated by the coefficients and voltage angle between the voltage vector and rotor position. The switching voltages from the calculated duty ratio can supply the proper torque and flux to reduce the ripple and error. The proposed control scheme is verified through practical experimental comparisons.

Adaptive DC-link Voltage Control for Shunt Active Power Filter

  • Wang, Yu;Xie, Yun-Xiang
    • Journal of Power Electronics
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    • v.14 no.4
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    • pp.764-777
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    • 2014
  • This study analyzes the mathematical relationship between DC-link voltage and system parameters for shunt active power filters (APFs). Analysis and mathematical deduction are used to determine the required minimum DC-link voltage for APF. A novel adaptive DC-link voltage controller for the three-phase four-wire shunt APF is then proposed. In this controller, the DC-link voltage reference value will be maintained at the required minimum voltage level. Therefore, power consumption and switching loss will effectively decrease. The DC-link voltage can also adaptively yield different DC-link voltage levels based on different harmonic currents and grid voltage levels and thus avoid the effects of harmonic current and grid voltage fluctuation on compensation performance. Finally, representative simulation and experimental results in a three-phase four-wire center-split shunt APF are presented to verify the validity and effectiveness of the minimum DC-link voltage design and the proposed adaptive DC-link voltage controller.

Voltage control of distribution substation using fuzzy inference (퍼지추론을 이용한 배전변전소의 전압제어)

  • Kim, Hong-Gyun;Kim, Sung-Soo;Choi, Jae-Gyun;Park, Jong-Keun
    • Proceedings of the KIEE Conference
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    • 1996.07b
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    • pp.814-816
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    • 1996
  • This paper proposes a new voltage control method of distribution substation using fuzzy inference. The aims of distribution voltage control equipments are reducing the operation frequency of lap changers and improving the characteristics of voltage(decreasing the errors between the actual voltage and the reference voltage). However, these objectives are in a trade-off relationship. Conventional voltage control equipment does not have functions of judgement and prediction, so it turns up limitations of voltage control. Proposed voltage control method using fuzzy inference can improve voltage characteristics as it has those functions of judgement and prediction. This paper describes the design method of new voltage control method using fuzzy inference, simulates with simple voltage and current models, and compares decreased voltage errors with conventional voltage errors.

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Fabrication and Evaluation of AC 400 kV High Voltage Divider using Electric Field Sensor (전기장 센서를 이용한 교류 400 kV 고전압 분압기의 제작 및 평가)

  • Lee, Sang-Hwa;Han, Sang-Gil;Jung, Jae-Kap;Kang, Jeon-Hong;Kim, Yoon-Hyoung;Jeong, Jin-Hye;Han, Sang-Ok
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.57 no.3
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    • pp.265-269
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    • 2008
  • Output voltage value of AC high voltage source has usually been obtained by measuring the low arm voltage of high voltage divider or the secondary voltage of high voltage transformer. In this study, we have fabricated the AC 400 kV high voltage divider using high voltage electrode and electric field measurement sensor. The dividing ratio of the fabricated 400 kV high voltage divider was evaluated using reference 400 kV capacitive divider. The dividing ratio of 400 kV high voltage divider is found to be 12,322 and has the good linearity within 0.63 % against AC high voltage up to 400 kV. Therefore, the developed 400 kV high voltage divider could evaluate 400 kV high voltage supply and voltage divider used in industry.

Target Operation Voltage Guidelines Considering Voltage Level in Each Voltage Control area by Applying Optimization Technique Through EMS Data Observation (EMS data 분석 및 최적화 기법을 적용한 제어지역별 목표운전전압 제안)

  • Sung, Ung;Kim, Jae-Won;Kim, Tae-Gyun;Lee, Byong-Jun;Jung, Eung-Soo;Cho, Jong-Man
    • The Transactions of The Korean Institute of Electrical Engineers
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    • v.58 no.4
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    • pp.671-678
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    • 2009
  • This paper presents target operation voltage guidelines of each voltage control area considering both voltage stability and economical efficiency in real power system. EMS(Energy Management System) data, Real-time simulator, shows not only voltage level but lots of information about real power system. Also this paper performs optimal power flow calculation of three objective functions to propose the best target operation voltage. objective function of interchange power flow maximum and active power loss minimization stand for economical efficiency index and reactive power reserve maximum objective unction represents stability index. Then through simulation result using optimazation technique, the most effective objective function is chosen. To sum up, this paper divides voltage control area into twelve considering electric distance characteristics and estimate or voltage level by the passage of time of EMS peak data. And through optimization technique target operation voltage of each voltage control area is estimated and compare heir result. Then it is proposed that the best scenario to keep up voltage stability and maximize economical efficiency in real power system.

Threshold Voltage Dependence on Bias for FinFET using Analytical Potential Model

  • Jung, Hak-Kee
    • Journal of information and communication convergence engineering
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    • v.8 no.1
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    • pp.107-111
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    • 2010
  • This paper has presented the dependence of the threshold voltage on back gate bias and drain voltage for FinFET. The FinFET has three gates such as the front gate, side and back gate. Threshold voltage is defined as the front gate bias when drain current is 1 micro ampere as the onset of the turn-on condition. In this paper threshold voltage is investigated into the analytical potential model derived from three dimensional Poisson's equation with the variation of the back gate bias and drain voltage. The threshold voltage of a transistor is one of the key parameters in the design of CMOS circuits. The threshold voltage, which described the degree of short channel effects, has been extensively investigated. As known from the down scaling rules, the threshold voltage has been presented in the case that drain voltage is the 1.0V above, which is set as the maximum supply voltage, and the drain induced barrier lowing(DIBL), drain bias dependent threshold voltage, is obtained using this model.