• Title/Summary/Keyword: Positive and negative sequence

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One-Cycle Control Strategy for Dual-Converter Three-Phase PWM Rectifier under Unbalanced Grid Voltage Conditions

  • Xu, You;Zhang, Qingjie;Deng, Kai
    • Journal of Power Electronics
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    • v.15 no.1
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    • pp.268-277
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    • 2015
  • In this paper, a dual-converter three-phase pulse width modulation (PWM) rectifier based on unbalanced one-cycle control (OCC) strategy is proposed. The proposed rectifier is used to eliminate the second harmonic waves of DC voltage and distortion of line currents under unbalanced input grid voltage conditions. The dual-converter PWM rectifier employs two converters, which are called positive-sequence converter and negative-sequence converter. The unbalanced OCC system compensates feedback currents of positive-sequence converter via grid negative-sequence voltages, as well as compensates feedback currents of negative-sequence converter via grid positive-sequence voltages. The AC currents of positive- and negative-sequence converter are controlled to be symmetrical. Thus, the workload of every switching device of converter is balanced. Only one conventional PI controller is adopted to achieve invariant power control. Then, the parameter tuning is simplified, and the extraction for positive- and negative-sequence currents is not needed anymore. The effectiveness and the viability of the control strategy are demonstrated through detailed experimental verification.

A Study on the Detection of Unbalanced Voltages for Instantaneous Voltage Compensation (순시전압 보상을 위한 불평형 전압 검출기법에 관한 연구)

  • Jeong, Hong-Ju;Choe, Si-Yeong;Jeong, Jun-Mo;Song, Jong-Hwan
    • The Transactions of the Korean Institute of Electrical Engineers B
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    • v.51 no.4
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    • pp.203-209
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    • 2002
  • This paper presents a new control scheme for a DVR(Dynamic Voltage Restorer) system consisting of series voltage source PWM converters. To control negative sequence component of source voltage the detection of negative sequence is necessary. Generally, filtering process is used tn do that. Through this filtering process has some problems. This paper suggests a new method of separating positive and negative sequences. This control system is designed using differential controllers and digital filters, and positive sequence and negative sequences are controlled respectively. The performance of the presented controller and scheme are confirmed through simulation and actual experiment by 2.5kVA prototype DVR.

A Study on DVR Control for Unbalanced Voltage Compensation

  • Jung Hong-Ju;Suh In-Young;Kim Byung-Seob;Kim Rae-Young;Choi See-Young
    • Proceedings of the KIPE Conference
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    • 2001.10a
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    • pp.803-807
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    • 2001
  • This paper presents a new control scheme for a DVR (Dynamic Voltage Restorer) system consisting of series voltage source PWM converters. To control the negative sequence components of the source, it is necessary to detect the negative sequence components. Generally, a filtering process is used which has some undesirable effects. This paper suggests a new method for separating positive and negative sequences components. This control system is designed using differential controllers and digital filters. The positive and negative sequences are extracted and controlled individually. The performance of the presented controller and scheme are confirmed through simulation and actual experiment with a 2.5kVA prototype DVR system.

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Fault Phase Selection Algorithm using Unit Vector of Sequence Voltages for Transmission Line Protection (대칭분 전압 단위 벡터를 이용한 송전선로 보호용 고장상 선택 알고리즘)

  • Lee, Myeong-Su;Lee, Jae-Gyu;Kim, Su-Nam;Yu, Seok-Gu
    • The Transactions of the Korean Institute of Electrical Engineers A
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    • v.51 no.9
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    • pp.460-466
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    • 2002
  • A reliable fault phase selection algorithm plays a very important role in transmission line protection, Particularly in Extra High Voltage (EHV) networks. The conventional fault phase selection algorithm used the phase difference between positive and negative sequence current excluding load current. But, it is difficult to pick out only fault current since we can not know when a fault occurs and select the fault phase in weak-infeed conditions that dominate zero-sequence current in phase current. The proposed algorithm can select the accurately fault phase using the sum of unit vectors which are calculated by positive-sequence voltage and negative-sequence voltage.

Current Limit Strategy of Voltage Controller of Delta-Connected H-Bridge STATCOM under Unbalanced Voltage Drop

  • Son, Gum Tae;Park, Jung-Wook
    • Journal of Electrical Engineering and Technology
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    • v.13 no.2
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    • pp.550-558
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    • 2018
  • This paper presents the current limit strategy of voltage controller of delta-connected H-bridge static synchronous compensator (STATCOM) under an unbalanced voltage fault event. When phase to ground fault happens, the feasibility to heighten the magnitude of sagging phase voltage is considered by using symmetric transformation method in delta-structure STATCOM. And the efficiency to cover the maximum physical current limit of switching device is considered by using vector analysis method that calculate the zero sequence current for balancing the cluster energy in delta connected H-bridge STATCOM. The result is simple and obvious. Only positive sequence current has to be used to support the unbalanced voltage sag. Although the relationship between combination of the negative sequence voltage with current and zero sequence current is nonlinear, the more negative sequence current is supplying, the larger zero sequence current is required. From the full-model STATCOM system simulation, zero sequence current demand is identified according to a ratio of positive and negative sequence compensating current. When only positive sequence current support voltage sag, the least zero sequence current is needed.

Analysis and Control of Instantaneous Voltage Compensator Using New Phase Angle Detection Method Synchronized by Positive Sequence of Unbalanced 3-Phase Source (3상 불평형 전원 시스템의 새로운 위상각 검출기법을 이용한 순간전압보상기의 해석 및 제어)

  • 이승요;고재석;목형수;최규하
    • The Transactions of the Korean Institute of Power Electronics
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    • v.4 no.3
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    • pp.275-284
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    • 1999
  • Unbalanced source voltage in the 3-phase power system is decomposed into positive, negative and zero sequence c components. Also, assuming there is no neutral path in the system, the zero sequence component is not shown on the l load side. Therefore, in the unbalanced power system without neutral path. it is possible to provide balanced voltage to t the load side by compensating negative sequence component and also to regulate the voltage amplitude by controlling t the positive sequence component. In addition, the symmetrical components due to voltage unbalance can be effectively d detected on the synchronous reference frame by using dlongleftarrowq transformation. In this paper, an algorithm not only c compensating unbalanced source voltage by canceling the negative sequence component on the synchronous reference f frame but also maintaining load voltages constantly is proposed. Also a novel method for phase angle detection s synchronized by positive sequence component under unbalanced source voltage is suggested and this detected phase a angle is used for d-q transformation. The performances and characteristics of the proposed compensating system are a analyzed by simulation and verified through experimental results.

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An Integrated Compensation Algorithm for PCC Voltage Fluctuation and Unbalance with Variable Limit of Positive and Negative Sequence Currents

  • Im, Ji-Hoon;Song, Seung-Ho;Cho, Sung-Min
    • Journal of Electrical Engineering and Technology
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    • v.12 no.2
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    • pp.751-760
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    • 2017
  • This paper proposes a point of common coupling (PCC) voltage compensation algorithm using a current limitation strategy for use in distributed generation (DG). The proposed strategy maintains the PCC voltage by prioritizing currents when an output current reference is larger than the current capacity of the power condition system (PCS) of the DG. With this strategy, the DG outputs the active current, reactive current, and the negative sequence current. The DG uses the reactive current for maintaining the PCC voltage within a normal range; the negative sequence current is used for reducing the PCC voltage unbalance. The proposed method was verified using PSIM simulation and experimental results.

Current Control in Cascaded H-bridge STATCOM for Electric Arc Furnaces (전기로용 다단 H-브릿지 STATCOM의 전류제어)

  • Kwon, Byung-Ki;Jung, Seung-Ki;Kim, Tae-Hyeong;Kim, Yun-Hyun
    • The Transactions of the Korean Institute of Power Electronics
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    • v.20 no.1
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    • pp.19-30
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    • 2015
  • A static synchronous compensator (STATCOM) applied to rapidly changing, highly unbalanced loads such as electric arc furnaces (EAFs), requires both positive-sequence and negative-sequence current control, which indicates fast response characteristics and can be controlled independently. Furthermore, a delta-connected STATCOM with cascaded H-bridge configuration accompanying multiple separate DC-sides, should have high performance zero-sequence current control to suppress a phase-to-phase imbalance in DC-side voltages when compensating for unbalanced load. In this paper, actual EAF data is analyzed to reflect on the design of current controllers and a pioneering zero-sequence current controller with a superb transient performance is devised, which generates an imaginary -axis component from the presumed response of forwarded reference. Via simulation and experiments, the performance of the positive, negative, and zero-sequence current control of a cascaded H-bridge STATCOM for EAF is verified.

Cloning and Sequence Analysis of a Levansucrase Gene from Rahnella aquatilis ATCC15552

  • Kim, Hyun-Jin;Yang, Ji-Young;Lee, Hyeon-Gye;Cha, Jae-Ho
    • Journal of Microbiology and Biotechnology
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    • v.11 no.4
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    • pp.693-699
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    • 2001
  • An intracellular levansucrase gene, lscR from Rahnella aquatilis ATCC 15552, was cloned and its nucleotide sequence was determined. Nucleotide sequence analysis of this gene revealed a 1,238 bp open reading frame coding for a protein of 415 amino acids. The levansucrase was expressed by using a T7 promoter in Escherichia coli BL21 (DE3) and the enzyme activity was detected in the cytoplasmic fraction. The optimum pH and temperature of this enzyme for levan formation was pH 6 and $30^{\circ}C$, respectively. The deduced amino acid sequence of the lscR gene showed a high sequence similarity (59-89%) with Gram-negative levansucrses, while the level of similarity with Gram-positive enzymes was less than 42%. Multiple alignments of levansucrase sequences reported from Gram-negative and Gram-positive bacteria revealed seven conserved regions. A comparison of the catalytic properties and deduced amino acid sequence of lscR with those of other bacterial levansucrases strongly suggest that Gram-negative and Gram-positive levansucrases have an overall different structure, but they have a similar structure at the active site.

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Equivalent Grid Impedance Estimation Method Using Negative Sequence Current Injection in Three-Phase Grid-connected Inverter (3상 계통 연계형 인버터의 역상분 전류 주입을 이용한 계통 등가 임피던스 추정 기법)

  • Park, Chan-Sol;Song, Seung-Ho;Im, Ji-Hoon
    • The Transactions of the Korean Institute of Power Electronics
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    • v.20 no.6
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    • pp.526-533
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    • 2015
  • A new algorithm is proposed for the estimation of equivalent grid impedance at the point of common coupling of a grid-tie inverter output. The estimated impedance parameter can be used for the improvement of the performance and the stability of the distributed generation system. The estimation error is inevitable in the conventional estimation method because of the axis rotation due to PLL. In the conventional estimation error, the d-q voltage and current are used for the calculation of the impedance with active and reactive current injections. Conversely, in the proposed algorithm, the negative sequence current is injected, and then the negative sequence voltage is measured for the impedance estimation. As the positive and negative sequence current controller is independent and the PLL is based on the positive sequence component only, the estimation of the equivalent impedance can be achieved with high accuracy. Simulation and experimental results are compared to validate the proposed algorithm.