• Title/Summary/Keyword: nonlinear voltage distortion

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Suppression of Leakage Current and Distortion in Variable Capacitance Devices and their Application to AC Power Regulators

  • Katsuki, Akihiko;Oki, Takuya
    • Journal of Power Electronics
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    • v.16 no.1
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    • pp.66-73
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    • 2016
  • The quantity of alternating current (AC) leakage and the value of distortion factor in capacitor currents are discussed with regard to a new power component called variable capacitance device (VCD). This component has terminals for controlling its capacitance. Nonlinear dielectric characteristics are utilized in this device to vary the capacitance. When VCD operates in an AC circuit, the AC leakage from this device through direct current (DC) control voltage source increases according to the conditions of DC control voltage and so on. To solve this problem, we propose techniques for suppressing AC leakage. Although VCD has strong nonlinear characteristics, the current through the capacitor is not distorted significantly. The relations between AC leakage and the distortion in current waveforms are investigated. An application example for an AC power regulator is also introduced to evaluate the distortion in waveforms.

Analysis on the Harmonics Characteristics Due to Increase & Decrease of Nonlinear Load (비선형 부하의 증감에 따른 고조파 특성 분석)

  • Kim, Jong-Gyeum;Lee, Eun-Woong
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.52 no.3
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    • pp.100-106
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    • 2003
  • The increasing application of power electronic equipment in industrial field has led to a growing concern for harmonic distortion and the resulting impacts on system equipment and operations. Harmonic currents are generated by the operation of nonlinear loads and equipment on the power system. These are more increased by unbalance voltage of electrical distribution power systems. This paper describes harmonics characteristics generated by varying of nonlinear load at the PCC under the voltage unbalance.

Dead Time Compensation of Stand-alone Inverter Under Unbalanced Load (불평형부하 시 독립형 인버터의 데드타임 보상기법)

  • Jeong, Jinyong;Jo, Jongmin;Lee, Junwon;Chae, Woo-Kyu;Cha, Hanju
    • The Transactions of the Korean Institute of Power Electronics
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    • v.20 no.2
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    • pp.115-121
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    • 2015
  • Stand-alone inverter supplies constant voltage to loads. However, when a three-phase stand-alone inverter supplies unbalanced load, the generated output voltages also become unbalanced. The nonlinear characteristics of inverter dead time cause a more serious distortion in the output voltage. With unbalanced load, voltage distortion caused by dead time differs from voltage distortion under balanced load. Phase voltages in the stationary reference frame include unbalanced odd harmonics and then, d-q axis voltages in the synchronous reference frame have even harmonics with different magnitude, which are mitigated by the proposed multiple resonant controller. This study analyzes the voltage distortion caused by unbalanced load and dead time, and proposes a novel dead time compensation method. The proposed control method is tested on a 10-kW stand-alone inverter system, and shows that total harmonic distortion (THD) is reduced to 1.5% from 4.3%.

A study on the effect of inverter nonlinear characteristic on the flux estimation of an induction motor (인버터의 비선형 특성이 유도전동기의 자속 추정에 미치는 영향에 대한 연구)

  • Kim, Sang-Hoon;Kim, Tae-Suk
    • Journal of Industrial Technology
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    • v.28 no.B
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    • pp.167-174
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    • 2008
  • In this paper, the analysis on type effect of inverter output voltage distortion on the control of an induction motor is discussed. The inverter output voltage is distorted differently from the reference voltage owing to the inverter nonlinear characteristic. The inverter nonlinear characteristic results from the voltage drop, the inherent characteristic of the power semiconductor, and the dead time for preventing the short circuit of the inverter leg. This characteristic distorts the inverter output voltage and then, causes the motor flux estimation error. Although this characteristics do not significantly effect in the general-purpose induction motor control, but significantly effect on the low-speed operation of high performance motor control such as the sensorless vector control.

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Effective Voltage Quality Control under Nonlinear Loads in Islanded Microgrid (독립형 마이크로그리드에서 비선형 부하에 대한 고품질 전압제어)

  • Dam, Hung D.;Lee, Hong-Hee
    • The Transactions of the Korean Institute of Power Electronics
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    • v.21 no.6
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    • pp.465-472
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    • 2016
  • A nonlinear load causes harmonic distortion and hampers the performance of other loads or distributed generation (DG) sources connected to the point of common coupling (PCC). This study proposes a new control strategy to reduce harmonic components, such as fifth and seventh harmonics, at the PCC under nonlinear loads in islanded microgrids, which comprise more than two DG sources. The proposed control scheme enables the DG source to share the power commanded by the control center as well as to compensate for the voltage harmonics at the PCC. The reference current is estimated from the voltage harmonics and injecting power; thus, the control scheme is implemented without any additional hardware devices. The simulation and experimental results are presented to verify the effectiveness of the proposed control method.

Characteristic Analysis of Power Compensation Condenser Considering Voltage Harmonics (전압 고조파를 고려한 역률보상용 콘덴서의 특성 분석)

  • Kim, Jong-Gyeum;Lee, Dong-Ju
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.59 no.2
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    • pp.141-145
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    • 2010
  • Most of the industrial loads includes the non-linear load as well as the linear load because there are many kinds of power conversion equipments at the input stage of the load in distribution network. The non-linear load causes the distortion of voltage waveform at PCC because the non-linear load generates the harmonic current. As a result, various voltage harmonics are existed at PCC depending on the current harmonics from the non-linear load. And, a series reactor is generally connected to the power capacitor in series to attenuate the distortion of voltage waveform and to reduce an inrush current of power capacitor. Also, harmonic current of power capacitor is highly dependent on the series reactor because it is operated with the power capacitor as a passive filter against nonlinear loads. Then, these capacitors might be damaged by the excessive voltage and current harmonic components. In this paper, we presented how to select the capacitor and series reactor to meet the requirement of the voltage distortion at PCC and analyzed the voltage, current and capacity rating of the power capacitor by the computer simulation to ensure the safe operation of power capacitor when the voltage harmonics at PCC are existed. Also, the analysis data were compared with the experimental measurements for the verification.

Analysis of Volatage and Current Waveform Distortion Characteristics at Office Buildings (사무용 빌딩에서의 전압 및 전류파형 왜곡특성 분석)

  • Yoo, Jae-Geun;Lee, Sang-lck;Jeon, Jeong-Chay;Jeong, Jong-Wook;Lim, Young-Bae
    • Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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    • v.19 no.1
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    • pp.155-161
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    • 2005
  • Nonlinear electronic loads used at office buildings distort the voltage and current waveform that cause the overheating of transformer losses, ELB(Electrical Leakage Breaker) tripping, and so on. This paper analyzed waveform distortion characteristics at several once buildings by comparing with magnitude of voltage and current harmonics, crest factor of voltage and current, phase voltage and current unbalance. As a consequence, severe current waveform distortion in phase and neutral line by harmonics and high current unbalance rates by unbalanced using of single loads among the three phases are investigated. The results of the study can be used in making decisions regarding reasonable and economical operating of loads at office buildings.

A Study on the Characteristic of Capacitor by Voltage and Current Harmonics (전압 및 전류 고조파에 의한 커패시터 동작 특성)

  • Kim, Jong-Gyeum;Park, Young-Jeen;Lee, Dong-Ju;Lee, Eun-Woong
    • The Transactions of the Korean Institute of Electrical Engineers P
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    • v.58 no.3
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    • pp.257-262
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    • 2009
  • Capacitor is basically used for the power-factor compensation and sometimes as the passive filter to reduce harmonics of nonlinear load. Since the impedance of capacitor is inversely proportional to the frequency. The harmonic current may result in the problems of voltage distortion and resonance. Capacitor has easily fall under by two harmonic components, a nonlinear load and a distorted utility voltage. The amplified harmonic current and voltage may damage power capacitor. Hence the pre-investigation of harmonic is needed before designing and application the power factor for reducing fault rate. In this paper, we analyzed that voltage and current with harmonics components act on the capacitor under the resonance condition. we concluded that both voltage and current harmonics have an bad effect on the capacitor and current harmonics is a bitter rather than effect by voltage harmonics.

Output LC Filter Design of Voltage Source Inverter Considering the Performance of Controller (제어기응답을 고려한 전압형 인버터의 출력 LC필터 설계)

  • Kim, Jae-Sig;Choi, Jae-Ho
    • Proceedings of the KIEE Conference
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    • 2000.07b
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    • pp.1077-1079
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    • 2000
  • In this paper. the design procedure of the inverter output filter is described. The transfer function of the filter output voltage to the load current is described with the capacitor value and the system time constant including the controller. This means that the relation between the filter capacitor value and the system time constant is given as the closed form. By using the above closed form. the capacitor value can be calculated with the system time constant which can be implemented practically not using the try and error method. And as the effect of the load current to the voltage distortion can be calculated from the closed form, it can be verified how much the voltage distortion is effected when the nonlinear load is connected.

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A Study on Measurement and Analysis of Harmonics in Substation (변전소 고조파 측정 및 분석에 관한 연구)

  • Han Mu-Ho;Park Tae-Joon;Lee Seung-Hee;Lee Chi-Hwan
    • Proceedings of the KIPE Conference
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    • 2001.07a
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    • pp.438-441
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    • 2001
  • Nonlinear loads change the sinusoidal nature of the ac power current, thereby resulting in the flow of harmonic currents in the ac power system that can cause interference with communication circuits and other type of equipment. To minimize the damage, it is needed to limit harmonics current and voltage. Harmonic measurement system was developed to measure individual voltage and current harmonic continuously and save harmonic data on computer. We measured all 154kV feeders in a steel making company substation. Voltage and current distortion limits for general transmission systems was suggested We found some feeders exceeded current distortion limits. As result voltage harmonic exceeded standard limits.

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