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1
Paithankar, Y. G., and S. R. Bhide. "A Fast Method for Sequence Component Filtering." International Journal of Electrical Engineering & Education 40, no. 1 (2003): 66–71. http://dx.doi.org/10.7227/ijeee.40.1.7.
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In this paper a method to filter or segregate sequence components, using minimal hardware is presented. The method does not involve phase shifts other than that of 90 degrees. Thus it can be implemented using very simple hardware or if implemented in software will need considerably less amount of processing. The method consists in first separating the zero sequence component. Then the zero sequence component is subtracted from the input signal to get a signal which is sum of positive and negative sequence components. Further it is pointed out that difference between positive and negative sequence components is easily found from the difference of the phase quantities. Thus the sum and difference of positive and negative sequence components are available, from which individual positive and negative sequence components can be easily separated by simple addition and subtraction operations.
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Zhang, Xiao Ying, Zheng Jiang, and Zhong Jian Zhou. "Three-Phase Magnitude Detection Based on Decoupling Positive and Negative Sequences of Double D-Q Transformation." Advanced Materials Research 765-767 (September 2013): 2101–4. http://dx.doi.org/10.4028/www.scientific.net/amr.765-767.2101.
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This paper introduces T/4 time-lapse elimination detection, a novel method of detecting three-phase magnitude based on double d-q synchronous reference frame, functioning in decoupling positive and negative sequences of fundamental wave. When the voltage (or current) fundamental positive and negative sequence components are separated, their magnitudes can be detected respectively, so it is effective to restrain the impact on detection precision from negative sequence component. To verify the performance of this novel method, simulation experiments like transient response under normal grid condition and dynamic response under three-phase unbalance with harmonic pollution condition is finished. The results indicate that the novel method obtains a high precision of measure and a better dynamic property and has advantages on preventing harmonic propagation compared with T/16 time-lapse elimination detection method. Thus it can be wildly applied in three-phase power electronic devices.
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Yang, Zonglei, Chao Xie, and Chunya Yin. "Fault Location Method for Distribution Network Using an Additional Inductance Strategy." Electronics 13, no. 4 (2024): 712. http://dx.doi.org/10.3390/electronics13040712.
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In distribution networks, time asynchrony exists between the phasor measuring unit (PMU) at both ends of a line, and the effective measurement time of the devices is short, leading to insufficient accuracy in phasor measurements. This paper proposes a fault location method for distribution networks that employ an additional inductance strategy to address the limited location accuracy caused by time asynchrony and the inadequate accuracy of phasor measurement devices. The method enhances the stability and accuracy of phase measurement by connecting an additional inductance after the online circuit breaker, thus extending the effective measurement time. It uses the symmetrical component method to obtain the positive-sequence and negative-sequence networks following a fault. Time asynchrony is treated as an equivalent asynchronous phase angle, which is then applied to the positive and negative-sequence voltage components. The impact of time asynchrony is mitigated by compensating for the phase angle difference using the ratio of the positive-sequence voltage component to the negative-sequence voltage component. This approach provides the fault location function and has improved the accuracy of fault location, which is advantageous for rapid fault repair.
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Bialobrzheskyi, O., A. Postil, and S. Yakimets. "Accounting for a positive, negative and zero sequences power in a three-phase unbalanced electrical system." Naukovyi Visnyk Natsionalnoho Hirnychoho Universytetu, no. 6 (December 23, 2023): 93–99. http://dx.doi.org/10.33271/nvngu/2023-6/093.
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Purpose. Based on the instantaneous electrical power of a three-phase asymmetric system of sinusoidal periodic current, to determine positive, negative, zero-sequences active and reactive power, as well as invariance power factor. Methodology. In the unbalance case in three-phase electrical system, the electrical energy quality is evaluated by means on voltage and current positive, negative, zero-sequences. At the same time, similar components of active and reactive power have not received practical distribution. But it is precisely in terms of power that electricity is accounted for. The instantaneous power orthogonal components in the time domain are determined using the symmetrical components of voltage and current. Active, reactive powers of positive, negative and zero-sequences are allocated. The result obtained has the property of representativeness, which most of the known results lack. Findings. The three-phase system’s instantaneous power components are analytically determined, including the amplitudes of the oscillating power components. The need to take into account the oscillating instantaneous power components has been proven by means of a graphical interpretation of a special case of the three-phase system mode. As an integral indicator that takes into account the oscillating components of the three-phase system instantaneous power, its root-mean-square value over the repetition period is used. Originality. By calculating the transformer efficiency of the studied model according to the active power positive sequence and the same indicator according to the active power as a whole, it was established, that the component sequence separation affects the results of calculating the generalized indicators, including the power transmission system objects. This can lead to erroneous judgments about the efficiency of the specified facilities functioning. Practical value. The invariance power factor was used to characterize the electrical energy quality level of a three-phase sinusoidal current system in an unbalanced mode.
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Feng, Guoli, Zhihao Ye, Yihui Xia, Liming Huang, and Zerun Wang. "Impedance Modeling and Stability Analysis of Three-Phase Four-Wire Inverter with Grid-Connected Operation." Energies 15, no. 8 (2022): 2754. http://dx.doi.org/10.3390/en15082754.
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With the continuous penetration and development of renewable energy power generation, distributed grids and microgrids are becoming increasingly important in power systems. In the distribution networks and microgrids, the grid impedance is comparatively large and cannot be ignored. Usually, the parallel compensation is used to improve the grid quality. In these three-phase four-wire power systems, analyzing the impedance characteristics of the grid-connected inverter is vital to carry out the small-signal stability analysis. Thus, it is vital to consider the influence of the zero-sequence component in addition to the positive-sequence component and the negative-sequence component when it comes to analyzing system stability. In this paper, the impedances of three-phase four-wire split capacitor inverter and three-phase four-leg inverter are established. Based on the achieved impedance, the similarities and differences between the impedances of three-phase four-wire split capacitor inverter and impedance of three-phase four-leg inverter are studied. The main difference is reflected in zero-sequence impedance. Additionally, the zero-sequence impedance characteristics and the dominating factors deciding the zero-sequence impedance are analyzed. Then, the stability of the system considering the grid impedance and impedance of three-phase four-wire inverter is investigated by separately considering the stability of the positive–negative-sequence component and the stability of the zero-sequence component. Several cases of small-signal instability caused by the positive–negative-sequence component or zero-sequence component are revealed. The experimental results validate the theoretical analysis.
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Li, Dan, and Ting Ting Cai. "Control Strategy for VSC-HVDC under Unbalanced Grid Voltages." Applied Mechanics and Materials 863 (February 2017): 214–19. http://dx.doi.org/10.4028/www.scientific.net/amm.863.214.
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This paper describes the use of an unbalanced control strategy to solve the faults occur in AC grid side of High voltage direct current based on Voltage Source Converter (VSC-HVDC) system. This method divides the voltage and current parameters into negative-sequence and positive-sequence. It can be obtained that the negative-sequence appears as double-frequency component in the positive-sequence synchronous reference frame; while, it appears as dc component in the negative-sequence synchronous reference frame. To mitigate the unfavourable impact of the unbalance fault, such as the DC link ripples, the dual vector control algorithm in dq synchrounous reference frame is designed. Simulation results demonstrate the validity and the effectiveness of the proposed control scheme.
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Tian, Shiji, Min Lu, Ruikang Wang, and Di’an Liu. "Research on the Control Method of the PV Grid-Connected Inverter under an Asymmetrical Power Grid Fault." Energies 16, no. 22 (2023): 7504. http://dx.doi.org/10.3390/en16227504.
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The negative-sequence current component and harmonic components generated when an asymmetrical fault occurs in the power grid seriously affect the normal operation of the photovoltaic (PV) grid-connected inverter. In order to suppress the negative-sequence current component and the harmonic component of the grid-connected current, and to meet the normal grid-connected operation requirements of the PV grid-connected inverter when asymmetrical faults occur in the grid, this paper proposes the proportional integral double-resonant (PI-DR) current controller, which consists of the PI controller and double-resonant controllers. The PI-DR current controller can directly control the negative-sequence current component and the grid-connected current harmonic component in the output current in the forward synchronous rotating coordinate system, without decomposing the positive and negative sequence currents. The PI-DR current controller ensures that the PV grid-connected inverter can realize normal grid-connected operation and improves the quality of the power when an asymmetrical fault occurs in the power grid. MATLAB/Simulink experiments show that the PI-DR current controller can improve the dynamic characteristics of the PV grid-connected inverter and improve the operating capability of the system when an asymmetrical fault occurs in the power grid.
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Fu, Pengwu, Dongwen Yang, Zhi He, Zhenfeng Duan, and Dengmei Wang. "Practical calculation of asymmetric short circuit current of DFIG connected to distribution network." E3S Web of Conferences 145 (2020): 02075. http://dx.doi.org/10.1051/e3sconf/202014502075.
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In view of the existing complex analytic calculations of DFIG short-circuit current are hardly applied in engineering projects, a practical calculation of asymmetric short-circuit current of DFIG is proposed. According to the complex sequence and their Thevenin equivalent model of DFIG network, the composition of each sequence component of DFIG short-circuit current is analysed. Moreover, considering the low-voltage ride through strategy of DFIG, the negative sequence periodic components of short circuit current are well analysed during the crowbar activation and deactivation, and the formula of the negative sequence periodic components of short circuit current are derived. On the basis of positive and negative sequence open circuit voltage, calculating impedance and rotor current, the judgement of crowbar activation is established. The pre-calculated surfaces of negative sequence periodic components of short circuit current are proposed, and the procedure for calculating the asymmetric short-circuit current of DFIG is designed. Finally, the proposed method is verified by simulation.
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Wang, Yan, Dan Zhou, and Song Xiao Xu. "Study on Phase Comparison Pilot Protection for Six-Phase Transmission Lines Based on Six-Sequence Transformation." Advanced Materials Research 433-440 (January 2012): 2394–99. http://dx.doi.org/10.4028/www.scientific.net/amr.433-440.2394.
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Six-phase transmission system occupys a narrow line corridor, and it can also effectively improve power transmission density, so it gains more and more attention. A new scheme of phase comparison protection suitable for six-phase transmission lines was proposed in this paper. Because both ends of electrical quantities on six-phase transmission line are decoupled into six separate sequence components, of which opposite positive fault sequence component is independent with load current in typical six-phase transmission system, the scheme utilizes the sum of forementioned fault sequence components and same positive current sequence component and opposite negative current sequence component in proportion as the operating current in phase comparison pilot protection. The theoretical analysis and result of simulation confirm that the new scheme can correctly reflect any fault of the six-phase transmission lines, and it can overcome the disadvantages of the conventional protection under conditions of power swing, heavy load current and high transition resistances, and it can improve the sensitivity of phase comparison pilot protection and be used on six-phase transmission lines as main protection.
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Li, Wei, and Li Sun. "Grid Information Synchronous Monitoring Algorithm under Unbalanced and Distorted Condition." Advanced Materials Research 898 (February 2014): 867–72. http://dx.doi.org/10.4028/www.scientific.net/amr.898.867.
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The Amplitude and angular frequency of grid voltage vector fluctuate with the positive and negative sequence components and harmonic component under unbalance and distortion grid model, the conventional grid information synchronous algorithm is not suitable. A novel grid information synchronous algorithm based on AC amplitude integral is proposed, which can obtain the information of phase angle, frequency and amplitude of the fundamental positive and negative sequence components of fundamental grid voltage using the synchronization phase locked technique. Experimental results show that the proposed algorithm is suitable to the unbalanced and distorted grid condition and can restrain the harmonic interference and achieve the grid information synchronous monitoring.
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Ren, Yi, Jian Ru Wan, Li Guang Shi, and Ran Liu. "Double-Loop Control of Inverter with LCL Filter in Electrical Power System Based on Improved Instantaneous Symmetrical Component." Advanced Materials Research 676 (March 2013): 265–68. http://dx.doi.org/10.4028/www.scientific.net/amr.676.265.
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An improved instantaneous symmetrical component method is adopted to improve the performance of inverter with LCL filter under asymmetric voltage conditions in electrical power system. Positive and negative sequence components in voltage and current in electrical power system are calculated with fewer calculation time,which is suitable for pratical application.In addition,this paper analyses active and reactive power in the system.A double-loop control strategy is proposed to eliminate the influence of double frequency components in power and negative sequence current.The simulation results verify its feasibility and effectiveness.
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Khanal, Bibek, Kulchandra Bhattarai, Lenish Shrestha, Aashish Dahal, and Indraman Tamrakar. "Modeling of Grid Tied PV Inverter to Improve its Performance During Unbalanced Load and Unbalance Fault." KEC Journal of Science and Engineering 8, no. 1 (2024): 94–102. http://dx.doi.org/10.3126/kjse.v8i1.69275.
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Integrating solar through inverter brings about various challenges in the microgrids and the inverter itself. This paper aims to the study of problems in the operation of inverter during unbalance load and unbalance fault condition along with the possible control measures to mitigate those problems to ensure the safe and reliable operation of the inverter. A grid connected PV inverter is modeled using hysteresis band controller and implementing the MPPT of the PV system with the buck boost converter. During unbalance load and unbalance fault condition, the negative and zero sequence components of current exists. All the zero-sequence component of current is delivered by the grid. The negative sequence component of current also flows through the inverter resulting in high value of current and loss of stability. Also, the voltage across the dc link capacitor increases during fault. The high value of current flowing through the inverter and high voltage across dc link capacitor may damages the inverter and capacitor respectively. An inverter dual current controller is introduced replacing the hysteresis band control such that the negative sequence component of current flowing through the inverter is almost mitigated from 600A to 10A and positive sequence current is also reduced relatively to a tolerable value 150A from 550A. The total current flowing through the inverter is limited to 200A from 950A and voltage across dc link capacitor is limited to 700V from 1050V during LG fault at the inverter side thus ensuring safe operation of the inverter during voltage dip condition. A further study can be done on limiting the positive sequence component of current to a rated value and improving the performance while operating in islanded mode.
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Gnaciński, Piotr, Damian Hallmann, Piotr Klimczak, Adam Muc, and Marcin Pepliński. "Effects of Negative Sequence Voltage Subharmonics on Cage Induction Motors." Energies 15, no. 23 (2022): 8797. http://dx.doi.org/10.3390/en15238797.
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In some power systems, voltage waveforms contain, apart from harmonics, interharmonics and subharmonics that are components of frequency less than or not an integer multiple of the fundamental frequency. Voltage subharmonics and interharmonics may be of both a positive and negative sequence, independently of their frequency. Previous papers on induction motors under subharmonics have been generally limited to the components of a positive sequence. This study deals with the effect of negative sequence subharmonics on the work of induction motors. Investigations were performed using the 2D finite element method and an experimental method. Differences between the impact of positive and negative sequence subharmonics are discussed. It was found that negative sequence voltage subharmonics can result in significant current subharmonics, torque pulsations and vibration. Further, because of possible resonance, motors that are comparatively resistant to positive sequence subharmonics might be especially sensitive to negative sequence subharmonics of the same frequency and vice versa.
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Mostafa, Rida, Rashad Essam, El Samahy Adel, El Koroflly Mohamed, and Youssef Erhab. "Performance analysis of a stand-alone synchronous reluctance generator under unbalanced conditions." International Journal of Power Electronics and Drive Systems 14, no. 01 (2023): 140~152. https://doi.org/10.11591/ijpeds.v14.i1.pp140-152.
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A stand-alone self-excited wind energy conversion system (WECS) is considered commonly used in remote areas due to its simple control and low cost. This paper introduces the performance analysis of a stand-alone selfexcited reluctance generator (SERG) under balanced and unbalanced operations. An asymmetrical component is proposed to obtain the positive and negative sequence components of voltages and currents in addition to the unbalanced voltage factor of SERG. The obtained results have been validated and compared with experimental results obtained from a laboratory prototype of a 5.5 kW synchronous reluctance generator driven by a dc motor as a primemover under unbalanced excitation capacitors and unbalanced loads. The comparison verifies the applicability of the proposed model.
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Miyaoka, Masashi, Kazuhito Hatanaka, Masayuki Iwazaki, and Naoya Nakamura. "CK7/CK20 Double-Negative Pulmonary Enteric Adenocarcinoma With Histopathological Evaluation of Transformation Zone Between Enteric Adenocarcinoma and Conventional Pulmonary Adenocarcinoma." International Journal of Surgical Pathology 26, no. 5 (2018): 464–68. http://dx.doi.org/10.1177/1066896918756737.
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We report a rare case of pulmonary enteric adenocarcinoma (PEA) exhibiting a immunohistochemical feature of CK7/CK20 double-negativity by evaluating the transformation zone between PEA and conventional pulmonary adenocarcinoma (CPA). A 75-year-old man was found to have a mass, 40 mm in diameter, in the right lower lobe on chest computed tomography, and underwent right lower lobectomy. Histologically, the tumor was composed of a PEA and CPA component. The dominant PEA component had medium to large complex glands with tall columnar cells with eosinophilic cytoplasm and brush-border. The CPA component comprised small to medium glands with cuboidal cells. Moreover, intermediate glands (INT), which had cuboidal to tall columnar cells, with morphological features between PEA and CPA, was also observed in the transformation area. Immunohistochemically, the PEA component was negative for CK7, CK20, and TTF-1, and positive for CDX2 and SATB2 (weak): the CPA component was negative for CK20, CDX2, and SATB2, and positive for CK7 and TTF-1: the INT were negative for SATB2, with intermingled positive signals for CK7, CK20, TTF-1, and CDX2. The final diagnosis was PEA based on the CPA component and not colorectal carcinoma. To distinguish CK7-negative PEA from metastatic colorectal carcinoma, careful examination for a CPA component is very useful along with clinical information. There are no reports that discuss about process of oncogenesis, de novo sequence or transformation from CPA of PEA. This is the first reported case of CK7/CK20 double-negative PEA, with analysis of the transformation zone between PEA and CPA components.
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Marcos Lobo da Fonseca, Jean, Francisco Kleber de Araújo Lima, Fernando Lessa Tofoli, and Carlos Gustavo Castelo Branco. "Three-phase phase-locked loop algorithms for the detection of positive-sequence and negative-sequence components." International Journal of Electrical Power & Energy Systems 126 (March 2021): 106570. http://dx.doi.org/10.1016/j.ijepes.2020.106570.
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Feng, Guoli, Zhihao Ye, Yihui Xia, Heng Nian, Liming Huang, and Zerun Wang. "High Frequency Resonance Suppression Strategy of Three-Phase Four-Wire Split Capacitor Inverter Connected to Parallel Compensation Grid." Energies 15, no. 4 (2022): 1486. http://dx.doi.org/10.3390/en15041486.
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With the continuous penetration and development of renewable energy power generation, the distributed grid and the microgrid are becoming increasingly important in modern power systems. In distribution networks and the microgrid, the grid impedance is comparatively large and cannot be ignored. Usually, the parallel compensation is used to improve the grid quality. In the grid with parallel compensation, the large phase angle difference between the impedance of the grid-connected inverter and the impedance of the grid at amplitude intersection will result in high frequency resonance (HFR). Because the inverter shows filter characteristics due to limited bandwidth of the controller, the parallel compensation grid, respectively, performs as the capacitance characteristic and inductance characteristic in different high frequency range. Compared with the three-phase, three-wire system, an additional zero-sequence path exists in the three-phase four-wire split capacitor inverter (TFSCI) system, so that the existing high frequency resonance suppression methods will be not effective. Since the zero-sequence component is neglected, HFR will also occur, in addition to the positive-sequence component and the negative-sequence component. Therefore, in order to suppress the high frequency resonance caused by positive-sequence, negative-sequence and zero-sequence components, an impedance reshaping strategy based on current feedback is proposed in this paper. This proposed method can reshape the amplitude and phase of the inverter impedance in a high frequency range without affecting the performance of the fundamental frequency control and ensure that the inverter contains a sufficient phase margin. Additionally, the proposed method can reshape the impedance of TFSCI within a wide frequency range, which makes it able to cope with the challenge of the parallel compensation degree change. Theoretical analysis and experiments verify the availability of the proposed control strategy.
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Smits, Theo H. M., Stefanie B. Balada, Bernard Witholt, and Jan B. van Beilen. "Functional Analysis of Alkane Hydroxylases from Gram-Negative and Gram-Positive Bacteria." Journal of Bacteriology 184, no. 6 (2002): 1733–42. http://dx.doi.org/10.1128/jb.184.6.1733-1742.2002.
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ABSTRACT We have cloned homologs of the Pseudomonas putida GPo1 alkane hydroxylase from Pseudomonas aeruginosa PAO1, Pseudomonas fluorescens CHA0, Alcanivorax borkumensis AP1, Mycobacterium tuberculosis H37Rv, and Prauserella rugosa NRRL B-2295. Sequence comparisons show that the level of protein sequence identity between the homologs is as low as 35%, and that the Pseudomonas alkane hydroxylases are as distantly related to each other as to the remaining alkane hydroxylases. Based on the observation that rubredoxin, an electron transfer component of the GPo1 alkane hydroxylase system, can be replaced by rubredoxins from other alkane hydroxylase systems, we have developed three recombinant host strains for the functional analysis of the novel alkane hydroxylase genes. Two hosts, Escherichia coli GEc137 and P. putida GPo12, were equipped with pGEc47ΔB, which encodes all proteins necessary for growth on medium-chain-length alkanes (C6 to C12), except a functional alkane hydroxylase. The third host was an alkB knockout derivative of P. fluorescens CHA0, which is no longer able to grow on C12 to C16 alkanes. All alkane hydroxylase homologs, except the Acinetobacter sp. ADP1 AlkM, allowed at least one of the three hosts to grow on n-alkanes.
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Dr., M. Mohammadha Hussaini, and G. Sureshkumar. "SPWM Triggered AC Voltage Controller for the Reduction of Lower Order Harmonics." Journal of Power Electronics and Drives 5, no. 1 (2020): 28–54. https://doi.org/10.5281/zenodo.3955720.
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Power electronic controllers are the major harmonic producing components. Lower order harmonics are very dangerous for transformers, induction motors, generators and other equipment’s. The filter design for the lower order harmonics is also a complex one. So the best way for the reduction of lower order harmonics is using pulse width modulation technique. The main abstract is to reduce the lower order and triplen harmonics which produce zero sequence components. The Crawling can be reduced using the PWM ac voltage controller. Third order harmonics is constant for all modulation index in PWM ac voltage controller, so filter design for 3rd order harmonics is easy and the cost of filter circuit is low.
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Han, Yanzan, and Jimeng Zhang. "Recognition Algorithm of Transient Overvoltage Characteristic Based on Symmetrical Components Estimation." Symmetry 12, no. 1 (2020): 114. http://dx.doi.org/10.3390/sym12010114.
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The recognition of transient overvoltage characteristics is the premise of disturbance compensation of the transient overvoltage. Based on that, the recognition algorithm of transient overvoltage characteristics based on symmetrical components estimation was proposed. The generation mechanism of the transient overvoltage in gas insulated switchgear (GIS) was analyzed. Then, the transient overvoltage was measured via the capacitive sensor method. The three-phase voltage of ultra-high voltage grid was asymmetrical when the transient overvoltage appeared. At present, the asymmetrical three-phase voltage was decomposed into the superposition of a symmetrical positive-sequence component, a negative-sequence component, and a zero-sequence component via the symmetrical components estimation to build the superposition model. The model was decomposed via the trigonometric identity and the modified neural network of the least mean square learning rule was used to estimate the parameter vector of the characteristic quantity of the transient overvoltage in real time. The feasibility of the proposed algorithm was verified via comparing the simulation of the proposed algorithm and the algorithm based on dp transformation. The experimental results show that the proposed algorithm has the advantages of a small operand, high detection precision, and fast action.
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Rasool, Akhtar, Esref Emre Ozsoy, Fiaz Ahmad, Asif Sabanoviç, and Sanjeevikumar Padmanaban. "Disturbance-observer based control of voltage-source-converter under unbalanced voltage conditions." World Journal of Engineering 14, no. 6 (2017): 522–31. http://dx.doi.org/10.1108/wje-01-2017-0021.
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Purpose This paper aims to propose a novel grid current control strategy for grid-connected voltage source converters (VSCs) under unbalanced grid voltage conditions. Design/methodology/approach A grid voltage dynamic model is represented in symmetrical positive and negative sequence reference frames. A proportional controller structure with a first-order low-pass filter disturbance observer (DOB) is designed for power control in unbalanced voltage conditions. This controller is capable of meeting the positive sequence power requirements, and it also eliminates negative sequence power components which cause double-frequency oscillations on power. The symmetrical components are calculated by using the second-order generalized integrator-based observer, which accurately estimates the symmetrical components. Findings Proportional current controllers are sufficient in this study in a wide range of operating conditions, as DOB accurately estimates and feed-forwards nonlinear terms which may be deteriorated by physical and operating conditions. This is the first reported scheme which estimates the VSC disturbances in terms of symmetrical component decomposition and the DOB concept. Originality/value The proposed method does not require any grid parameter to be known, as it estimates nonlinear terms with a first-order low-pass filter DOB. The proposed control system is implemented on a dSPACE ds1103 digital controller by using a three-phase, three-wire VSC.
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Wen, Ning, Hui Sun, Zhi Cheng Zhang, and Jin Tao Dai. "Research on STATCOM control strategy of Cascaded H-bridge considering unbalanced conditions." Journal of Physics: Conference Series 2338, no. 1 (2022): 012083. http://dx.doi.org/10.1088/1742-6596/2338/1/012083.
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Abstract STATCOM, a star cascade H bridge, usually uses zero-sequence voltage injection to achieve inter-phase DC voltage balance. Different from negative sequence current injection, the phase-to-phase DC voltage balance control based on zero sequence voltage injection does not generate zero sequence current in three-phase and three-wire systems, which is beneficial to the power quality of the system. In the traditional control algorithm, the zero sequence voltage is calculated by the unbalanced active power and current. The control algorithm contains a large number of complex operations and matrix operations, which need to consume a lot of controller resources and is not conducive to system design and expansion. Moreover, in order to improve the dynamic performance under voltage imbalance, the positive and negative sequence separation is introduced into the feedforward control to increase the complexity of the control algorithm. In order to simplify the control algorithm, a PI regulator is proposed to linearly adjust the DC component of zero sequence voltage in DQ coordinate system. At the same time, through theoretical analysis, it is found that the zero-sequence voltage in feedforward control is equal to the zero-sequence voltage in power grid, so the positive and negative sequence separation can be removed, further simplifying the algorithm.
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Osanyinpeju, Kifilideen. "DERIVATION OF FORMULAS OF THE COMPONENTS OF KIFILIDEEN TRINOMIAL EXPANSION OF POSITIVE POWER OF 𝑵 WITH OTHER DEVELOPMENTS". Journal of Science, Technology, Mathematics and Education (JOSTMED) 18, № 1 (2022): 77–97. https://doi.org/10.5281/zenodo.12596950.
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The sequence of the power combination of expansion of the Kifilideen trinomial theorem of positive power of 𝑛 is arranged in groups and patterns. Having a clearer view or picture of how the formulas of the components of the Kifilideen trinomial expansion were derived can lead to the discovery of formulating formulas for the series and sequences which follows the same pattern of progression as that of the trinomial expansion where series and sequence are not generated from trinomial expansion. Therefore, this study provides derivation for the formulas of the components of the Kifilideen trinomial expansion of positive power of 𝑛 with other development. The research work also inaugurated Kifilideen theorem of matrix transformation of Newton’s binomial theorem of positive and negative power of 𝑛 and – 𝑛 where 𝑎 and 𝑏 are found in parts of the Newton’s binomial expansion of the positive and negative power 𝑛 and – 𝑛. The idea of series and sequence were employed in developing the formulas of the components of the Kifilideen trinomial expansion of positive power of 𝑛. The study indicates that there are sequences and series that can be developed which are not trinomial based but have the same pattern in term of progression as that of the latter. The Kifilideen theorem would ease the method of obtaining the power combination of a given term of Newton’s binomial expansion in a systematic way.
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Yamashika, Herris, and Syafii Syafii. "Characteristics of symmetrical components for high impedance faults in distribution networks with photovoltaic inverters." Indonesian Journal of Electrical Engineering and Computer Science 33, no. 2 (2024): 727. http://dx.doi.org/10.11591/ijeecs.v33.i2.pp727-735.
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This work models a photovoltaic (PV) inverter connected to an IEC microgrid system. The purpose of this study was to find the characteristics of symmetrical components before and after a high impedance single phase short-circuit fault. The IEC microgrid system is tailored to the distribution system in Indonesia, where the applied voltage is 20 kV. Only parameters related to the short-circuit study are included in the model. A second-order generalized integrator frequency-locked-loop is utilized to represent the 3-phase PV inverter. The inverter model, previously treated as an ideal current source, and positive sequence current are no longer employed, as they fail to depict the characteristics of symmetric components during a phase-to-ground short-circuit fault. The IEC microgrid system connected to the PV inverter is simulated using ATPDraw-electro magnetic transient program (EMTP). Simulation results reveal that the changes in the symmetric component values of current after a fault experience a very insignificant increase. Meanwhile, the positive sequence voltage values following the short-circuit fault exhibit a negligible decrease. In contrast, the negative sequence and zero sequence voltage components after the short-circuit fault undergo a significant increase.
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Yamashika, Herris, and Syafii. "Characteristics of symmetrical components for high impedance faults in distribution networks with photovoltaic inverters." Indonesian Journal of Electrical Engineering and Computer Science 33, no. 2 (2024): 727–35. https://doi.org/10.11591/ijeecs.v33.i2.pp727-735.
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This work models a photovoltaic (PV) inverter connected to an IEC microgrid system. The purpose of this study was to find the characteristics of symmetrical components before and after a high impedance single phase short-circuit fault. The IEC microgrid system is tailored to the distribution system in Indonesia, where the applied voltage is 20 kV. Only parameters related to the short-circuit study are included in the model. A second-order generalized integrator frequency-locked-loop is utilized to represent the 3-phase PV inverter. The inverter model, previously treated as an ideal current source, and positive sequence current are no longer employed, as they fail to depict the characteristics of symmetric components during a phase-to-ground short-circuit fault. The IEC microgrid system connected to the PV inverter is simulated using ATPDraw-electro magnetic transient program (EMTP). Simulation results reveal that the changes in the symmetric component values of current after a fault experience a very insignificant increase. Meanwhile, the positive sequence voltage values following the short-circuit fault exhibit a negligible decrease. In contrast, the negative sequence and zero sequence voltage components after the short-circuit fault undergo a significant increase.
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Bellan, Diego. "Three-Phase Distortion Analysis based on Space-Vector Locus Diagrams." WSEAS TRANSACTIONS ON POWER SYSTEMS 18 (December 31, 2023): 467–73. http://dx.doi.org/10.37394/232016.2023.18.46.
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This work deals with the use of the space vector concept to characterize the harmonic content of a three-phase voltage/current. It is shown that the shape of the trajectory of the space vector on the complex plane (i.e., the locus diagram) provides information about its harmonic content. In particular, it is shown that each harmonic contributes to the locus diagram with a number of lobes depending on the relative angular frequency between the harmonic and the fundamental component. To this aim, the different contributions of positive-sequence and negative-sequence harmonics is explained and put into evidence with specific examples. The expressions for the magnitude and phase of the space vector as functions of the harmonics are derived analytically. Numerical examples are provided to show how the locus diagram can represent a three-phase quantity with positive-sequence and negative-sequence harmonics.
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Nor, Azizah Yusoff, M. Razali Azziddin, Abdul Karim Kasrul, and Jidin Auzani. "The direct power control of three-phase AC-DC converter under unbalance voltage condition." International Journal of Electrical and Computer Engineering (IJECE) 9, no. 6 (2019): 5107–14. https://doi.org/10.11591/ijece.v9i6.pp5107-5114.
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This paper presents the integrated approach for three-phase PWM AC-DC converter for obtaining the symmetrical components under unbalanced supply condition. In the cases of unbalanced three-phase system, it causes the presence of unbalanced current and voltages thus produce the negative components on the grid voltage. Otherwise, the unbalance voltage in a three-phase power system causes severe performance degradation of a grid connected VSI. Therefore, the input structures for conventional direct power control have been modified with a three simpler sequence networks instead it coupled by a detailed three-phase system method. Thus, the imbalance voltage can be resolved by separating from the individual elements of voltage and current into symmetrical components called as a sequence network. Consequently, the input power is relatively improved during unbalanced condition almost than 70%. It proven through the measurement of Total Harmonic Distortion (THD) from the conventional direct power control in individual elements is much higher compared than it resolved in separate components. Therefore, three symmetrical components are necessary for imbalance supply condition in order to obtaining the good quality of sinusoidal grid currents.
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Ni, Yi Feng, and Yong Qiang Zhu. "Dual-Current Loops Control Strategy of PWM Rectifier under Unbalanced Grid Voltage Conditions." Applied Mechanics and Materials 556-562 (May 2014): 2114–18. http://dx.doi.org/10.4028/www.scientific.net/amm.556-562.2114.
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The unbalanced grid voltage causes the current harmonics, the fluctuation of the active power in AC side and the fluctuation of the DC voltage. The dual-current loops control strategy can slove those problems. The positive and negative sequence components of grid voltages and currents were calculated based on the symmetrical component method and were used to calculate the instantaneous power in double dq rotate coordinate, which ratate at positive and negative synchronous angular velocity respectively. The dual-current loops control strategy was finally verified in simulation by comparing with the conventional synchronous PI current control. The simulation results show the dual-current loops control strategy is effective on eliminating the fluctuation of the active power in AC side and the fluctuation of the DC voltage.
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McGuire, Andrew T., Robert A. B. Keates, Stephanie Cook, and Dev Mangroo. "Structural modeling identified the tRNA-binding domain of Utp8p, an essential nucleolar component of the nuclear tRNA export machinery of Saccharomyces cerevisiae." Biochemistry and Cell Biology 87, no. 2 (2009): 431–43. http://dx.doi.org/10.1139/o08-145.
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Utp8p is an essential 80 kDa intranuclear tRNA chaperone that transports tRNAs from the nucleolus to the nuclear tRNA export receptors in Saccharomyces cerevisiae . To help understand the mechanism of Utp8p function, predictive tools were used to derive a partial model of the tertiary structure of Utp8p. Secondary structure prediction, supported by circular dichroism measurements, indicated that Utp8p is divided into 2 domains: the N-terminal beta sheet and the C-terminal alpha helical domain. Tertiary structure prediction was more challenging, because the amino acid sequence of Utp8p is not directly homologous to any known protein structure. The tertiary structures predicted by threading and fold recognition had generally modest scores, but for the C-terminal domain, threading and fold recognition consistently pointed to an alpha–alpha superhelix. Because of the sequence diversity of this fold type, no single structural template was an ideal fit to the Utp8p sequence. Instead, a composite template was constructed from 3 different alpha–alpha superhelix structures that gave the best matches to different portions of the C-terminal domain sequence. In the resulting model, the most conserved sequences grouped in a tight cluster of positive charges on a protein that is otherwise predominantly negative, suggesting that the positive-charge cleft may be the tRNA-binding site. Mutations of conserved positive residues in the proposed binding site resulted in a reduction in the affinity of Utp8p for tRNA both in vivo and in vitro. Models were also derived for the 10 fungal homologues of Utp8p, and the localization of the positive charges on the conserved surface was found in all cases. Taken together, these data suggest that the positive-charge cleft of the C-terminal domain of Utp8p is involved in tRNA-binding.
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Vershon, A. K., N. M. Hollingsworth, and A. D. Johnson. "Meiotic induction of the yeast HOP1 gene is controlled by positive and negative regulatory sites." Molecular and Cellular Biology 12, no. 9 (1992): 3706–14. http://dx.doi.org/10.1128/mcb.12.9.3706-3714.1992.
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The process of meiosis and sporulation in the yeast Saccharomyces cerevisiae is a highly regulated developmental pathway dependent on genetic as well as nutritional signals. The HOP1 gene, which encodes a component of meiotic chromosomes, is not expressed in mitotically growing cells, but its transcription is induced shortly after yeast cells enter the meiotic pathway. Through a series of deletions and mutations in the HOP1 promoter, we located two regulatory sites that are essential for proper regulation of HOP1. One site, called URS1H, brings about repression of HOP1 in mitotic cells and functions as an activator sequence in cells undergoing meiosis. The second site, which we designated UASH, acts as an activator sequence in meiotic cells and has similarity to the binding site of the mammalian CCAAT/enhancer binding protein (C/EBP). Both sites are required for full meiotic induction of the HOP1 promoter. We conclude that in mitotic yeast cells, the URS1H site maintains the repressed state of the HOP1 promoter, masking the effect of the UASH site. Upon entry into meiosis, repression is lifted, allowing the URS1H and UASH sites to activate high-level transcription.
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Vershon, A. K., N. M. Hollingsworth, and A. D. Johnson. "Meiotic induction of the yeast HOP1 gene is controlled by positive and negative regulatory sites." Molecular and Cellular Biology 12, no. 9 (1992): 3706–14. http://dx.doi.org/10.1128/mcb.12.9.3706.
Full textAbstract:
The process of meiosis and sporulation in the yeast Saccharomyces cerevisiae is a highly regulated developmental pathway dependent on genetic as well as nutritional signals. The HOP1 gene, which encodes a component of meiotic chromosomes, is not expressed in mitotically growing cells, but its transcription is induced shortly after yeast cells enter the meiotic pathway. Through a series of deletions and mutations in the HOP1 promoter, we located two regulatory sites that are essential for proper regulation of HOP1. One site, called URS1H, brings about repression of HOP1 in mitotic cells and functions as an activator sequence in cells undergoing meiosis. The second site, which we designated UASH, acts as an activator sequence in meiotic cells and has similarity to the binding site of the mammalian CCAAT/enhancer binding protein (C/EBP). Both sites are required for full meiotic induction of the HOP1 promoter. We conclude that in mitotic yeast cells, the URS1H site maintains the repressed state of the HOP1 promoter, masking the effect of the UASH site. Upon entry into meiosis, repression is lifted, allowing the URS1H and UASH sites to activate high-level transcription.
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Bendl, J., M. Chomat, and L. Schreier. "Independent control of positive- and negative-sequence current components in a doubly fed machine." European Transactions on Electrical Power 15, no. 3 (2005): 191–202. http://dx.doi.org/10.1002/etep.51.
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He, Wenwen, Jun Yao, Hao Xu, et al. "Transient Synchronous Stability Analysis of Grid-Forming Photovoltaic Grid-Connected Inverters during Asymmetrical Grid Faults." Energies 17, no. 6 (2024): 1399. http://dx.doi.org/10.3390/en17061399.
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Compared with the traditional grid-following photovoltaic grid-connected converter (GFL-PGC), the grid-forming photovoltaic grid-connected converter (GFM-PGC) can provide voltage and frequency support for power systems, which can effectively enhance the stability of power electronic power systems. Consequently, GFM-PGCs have attracted great attention in recent years. When an asymmetrical short-circuit fault occurs in the power grid, GFM-PGC systems may experience transient instability, which has been less studied so far. In this paper, a GFM-PGC system is investigated under asymmetrical short-circuit fault conditions. A novel Q-V droop control structure is proposed by improving the traditional droop control. The proposed control structure enables the system to accurately control the positive- and negative-sequence reactive current without switching the control strategy during the low-voltage ride-through (LVRT) period so that it can meet the requirements of the renewable energy grid code. In addition, a dual-loop control structure model of positive- and negative-sequence voltage and current is established for the GFM-PGC system under asymmetrical short-circuit fault conditions. Based on the symmetrical component method, the composite sequence network of the system is obtained under asymmetrical short-circuit fault conditions, and positive- and negative-sequence power-angle characteristic curves are analyzed. The influence law of system parameters on the transient synchronous stability of positive- and negative-sequence systems is quantitatively analyzed through the equal area criterion. Finally, the correctness of the theoretical analysis is verified by simulation and hardware-in-the-loop experiments.
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Ahmed, Hafiz, Zoheir Tir, Samet Biricik, and Mohamed Benbouzid. "Fundamental frequency sequence amplitude estimator for power and energy applications." PLOS ONE 17, no. 8 (2022): e0270851. http://dx.doi.org/10.1371/journal.pone.0270851.
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A grid-synchronization-based fundamental frequency positive-sequence (FFPS) and negative-sequence (FFNS) amplitudes estimation technique is proposed for unbalanced and distorted grid. In this technique, the sequence amplitudes are extracted by extracting the phase-angle of the FFPS and FFNS components. The extracted phase-angles have DC and double frequency AC components. The AC component is filtered out by using a Moving Average Filter (MAF) of appropriate window length. From the extracted phase-angle, the unknown frequency can be estimated by using a suitable controller. A frequency-fixed equidistant samples-based pre-loop filter is also applied to eliminate the effect of measurement offset. The proposed technique has a very simple structure and is easy to tune. Small-signal modeling-based stability analysis and gain tuning procedure are also provided. The proposed technique strikes a good balance between fast convergence and disturbance rejection capability. Comparative numerical simulation and experimental results with similar other techniques demonstrate the suitability and performance enhancement by the proposed technique.
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Valgardson, Jordan D., Sarah A. Struyvenberg, Zachary R. Sailer, et al. "Comparative Analysis and Ancestral Sequence Reconstruction of Bacterial Sortase Family Proteins Generates Functional Ancestral Mutants with Different Sequence Specificities." Bacteria 1, no. 2 (2022): 121–35. http://dx.doi.org/10.3390/bacteria1020011.
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Gram-positive bacteria are some of the earliest known life forms, diverging from gram-negative bacteria 2 billion years ago. These organisms utilize sortase enzymes to attach proteins to their peptidoglycan cell wall, a structural feature that distinguishes the two types of bacteria. The transpeptidase activity of sortases make them an important tool in protein engineering applications, e.g., in sortase-mediated ligations or sortagging. However, due to relatively low catalytic efficiency, there are ongoing efforts to create better sortase variants for these uses. Here, we use bioinformatics tools, principal component analysis and ancestral sequence reconstruction, in combination with protein biochemistry, to analyze natural sequence variation in these enzymes. Principal component analysis on the sortase superfamily distinguishes previously described classes and identifies regions of relatively high sequence variation in structurally-conserved loops within each sortase family, including those near the active site. Using ancestral sequence reconstruction, we determined sequences of ancestral Staphylococcus and Streptococcus Class A sortase proteins. Enzyme assays revealed that the ancestral Streptococcus enzyme is relatively active and shares similar sequence variation with other Class A Streptococcus sortases. Taken together, we highlight how natural sequence variation can be utilized to investigate this important protein family, arguing that these and similar techniques may be used to discover or design sortases with increased catalytic efficiency and/or selectivity for sortase-mediated ligation experiments.
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Quintero-Duran, Michell J., John E. Candelo-Becerra, and Johnny Posada. "Synchronizing a synchronverter to an unbalanced power grid using sequence component decomposition." Nonlinear Engineering 11, no. 1 (2022): 395–410. http://dx.doi.org/10.1515/nleng-2022-0043.
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Abstract The synchronverter is a device used in some microgrids to perform self-synchronization and represent the behavior of a synchronous machine. However, the original control has been proposed for balanced networks, which is not present in all distribution systems. In unbalanced networks, the negative sequence may appear and generate a double frequency oscillation when delivering power or a non-symmetrical current from the inverter; thus, it must compensate unbalanced load. Therefore, this article shows that a synchronverter can be synchronized using the positive sequence even when there are voltage unbalances. The proposed strategy was simulated in the Simulink-Matlab© software, considering an unbalanced power grid with a single inverter and a load. The results confirm the effectiveness of this strategy, as the synchronverter can follow the grid frequency and the wave shape amplitude after starting the frequency droop control.
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Shuo, Xu, Yang Bingyuan, and Li Dongsheng. "Analysis on the Applicability of Phase Selection Components of Inverter Power Supply Transmission Line." E3S Web of Conferences 204 (2020): 02007. http://dx.doi.org/10.1051/e3sconf/202020402007.
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This article analyzes the applicability of AC line phase selection components in the context of large-scale offshore wind farms through multi-terminal flexible direct transmission. When the AC line fails, the converter station adopts a control strategy to suppress negative sequence and only outputs positive sequence current, resulting The positive and negative sequence current distribution coefficients on the converter station side are seriously unequal; This leads to adaptability problems of traditional protection phase selection components, which may cause incorrect actions of reclosing, protection ranging and distance protection. The simulation results based on RTDS verify the correctness of the theoretical analysis.
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Suqueli García, M. F., M. A. Castellote, and P. M. Corva. "SEQUENCE ANALYSIS SUGGESTS POSITIVE SELECTION ON THE BOVINE PRODYNORPHIN GENE." Journal of Basic and Applied Genetics 31, Issue 2 (2020): 13–25. http://dx.doi.org/10.35407/bag.2020.31.02.02.
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Dynorphin A is an endogenous opioid peptide that is part of the KNDy system in the hypothalamus of mammals. This peptide acts as an inhibitor of the GnRH pulse generation, thus regulating the onset of puberty and reproductive cycles. The PDYN gene encodes the propeptide Prodynorphin, the precursor of Dynorphin A. Despite its physiological relevance, PDYN has not emerged as a candidate gene associated with puberty in genomic association studies conducted in cattle. The present work aimed to search for signatures of selection on the PDYN gene among cattle breeds. To this, the whole genome sequences from 57 samples of ten cattle breeds were used. The samples were grouped based on breed selection history and their productive differences, particularly in terms of sexual precocity. The population structure was analyzed using Principal Component Analyses. To evidence recent selection processes, neutrality tests, such as Tajima’s D and Fu & Li’s F* and D* were performed in defined functional regions of PDYN. The putative promoter of PDYN showed a population structure that is in agreement with the criteria considered to make the groups. In that region, neutrality tests were consistently negative and resulted in statistically significant for the dairy breeds. Also, these breeds exhibited less variability in the haplotype analyses than the others. The results presented here suggest that regulatory regions of PDYN could be under positive selection, particularly in dairy breeds. Key words: reproduction; KNDy neurons; Dynorphin; signatures of selection.
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Sheena, Latif, and J. S. Savier. "Control Strategy of Fault Current Limiting Phase Shifted DVR with RSC Dual Control Strategy for LVRT in DFIG." Journal of Control System and its Recent Developments 5, no. 2 (2022): 1–21. https://doi.org/10.5281/zenodo.7049946.
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<em>DFIG is the most popular Type 3 variable speed generator used for wind power extraction. The use of partially rated power electronic converters at the rotor side makes the DFIG highly sensitive to grid voltage disturbances. Occurrence of unsymmetrical faults at the stator side of DFIG introduces positive and negative sequence components in the rotor voltage and current. Unlike conventional FOC of RSC, a detailed control of both the sequence components is to be provided by the RSC during asymmetrical faults. Homogenous components present in the stator flux has to be reduced before RSC control can be enabled during LVRT. A Phase-Shifted Dynamic Voltage Restorer (PSDVR) is proposed in this paper for aiding the RSC to ride through homogenous rotor overcurrent during severe voltage dips. The DVR mode of PSDVR action ensures a safer reduction of homogenous rotor current component. This paper presents a theoretical simulation-based monitoring approach of RSC dual control supported with PSDVR in MATLAB/SIMULINK environment. Results justify the effectiveness of the proposed PSDVR method in supporting the RSC control during voltage unbalances occurring at the stator. Comparison of the proposed method with the existing topology also ensures stable operation of DFIG without the need for triggering crowbar circuitry. RSC dual sequence control enables negative sequence control and associated rotor current harmonics reduction. </em>
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El-Nagar, Mohammed, Khaled Ahmed, Eman Hamdan, Ayman S. Abdel-Khalik, Mostafa S. Hamad, and Shehab Ahmed. "Modified Extended Complex Kalman Filter for DC Offset and Distortion Rejection in Grid-Tie Transformerless Converters." Applied Sciences 13, no. 15 (2023): 9023. http://dx.doi.org/10.3390/app13159023.
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Proper operation of the grid-tie transformerless converters under unbalanced and distorted conditions entails a precise detection of the frequency and fundamental component of the grid voltage. One of the main problems that could arise during the estimation of grid parameters is the existence of a DC offset generated from measurement and A/D conversion. This undesirable induced DC offset could appear as a part of the reference sinusoidal current of grid-tie converters. Although literature has proposed the use of an extended complex Kalman filter (ECKF) for the estimation of positive and negative sequence voltage components as a promising competitor to phase locked loops, mitigating the effect of possible DC offsets when a Kalman filter is employed remains scarce. This paper proposes a new extended complex Kalman filter to improve the filter stability for estimating the frequency and the fundamental positive and negative symmetrical components of the grid voltages, where DC offset, scaling error, and noise can successfully be rejected. The theoretical findings are experimentally validated.
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Karaliunas, Bronius, and Edvardas Matkevicius. "Calculation of Spectrum Characteristics for Braking Modes of Linear Induction Motors." Solid State Phenomena 164 (June 2010): 41–46. http://dx.doi.org/10.4028/www.scientific.net/ssp.164.41.
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The purpose of the wok is to derive analytical expressions of spectral characteristics at electrical braking of linear induction motor with diverse number of poles as well as to provide results of calculations. The major task in the analysis of braking modes is to determine spectral characteristics of braking current, primary magnetic field and braking force. To this aim Maxwell equations were solved together with Fourier and Laplace integral transformations. The obtained results indicate that in addition to the main component of the magnetic field, when the space frequency is , in the process of braking there appears continuous spectrum of elementary components with the frequencies occupying the infinite sector from - to + . Due to that fact, during the process of energy conversion at the moment of braking, there participate positive – sequence, negative – sequence components and elementary components of the continuous spectrum, motionless in the space.
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Sun, Shao Hua, and Hong Qi Ben. "Modified Power Compensation Control Strategy of Three-Phase Grid-Connected Inverter under Unbalanced Grid Voltage Conditions." Applied Mechanics and Materials 740 (March 2015): 335–38. http://dx.doi.org/10.4028/www.scientific.net/amm.740.335.
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Control strategy under unbalanced grid voltage conditions is one of the most important issues for grid-connected inverter. Under unbalanced grid voltage conditions, the 2nd active and reactive power ripples generate, they pollute the grid. To meet the demands of IEEE Std.929-2000, this paper proposed a modified power compensation control strategy; the proposed solution is based on direct power control. To provide accurate compensating power, the power model of three-phase inverter under unbalanced grid voltage conditions is given, using the positive sequence current component and the negative sequence voltage component, the compensating powers are calculated in details. Theoretical analysis and comparative simulation verification are presented to demonstrate the effectiveness of the proposed control strategy.
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Dai, Zhiyong, Shuaishuai Lv, Julius K. Mwaniki, and Juxiang Zhang. "Global accurate estimation of positive‐ and negative‐sequence voltage components for variable frequency AC systems." IET Power Electronics 11, no. 10 (2018): 1730–37. http://dx.doi.org/10.1049/iet-pel.2017.0503.
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Xu, Feng, Xiaoming Huang, Yi Lu, and Zheren Zhang. "AC Fault Ride-Through Strategy of a Transformerless Soft Normally Open Point." Applied Sciences 12, no. 13 (2022): 6773. http://dx.doi.org/10.3390/app12136773.
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This paper focuses on the soft normally open point (SNOP) which has no transformers and connects to the 10 kV distribution network through the arc suppression coil grounding mode. A mathematical model containing positive-, negative-, and zero-sequence components under AC fault is established by the circuit analysis and the sequence component decomposition. Then the voltage fluctuation mechanism at the DC side and the non-fault AC side caused by the zero-sequence voltage on the fault side is analyzed under the case without transformers. Taking the single-phase grounding fault as an example, the fluctuation formula of the DC voltage and AC voltage is deduced in detail. Based on the theoretical analysis, the zero-sequence control strategy and the sub-module improvement strategy of the modular multilevel converter (MMC) are proposed. A back-to-back SNOP simulation model is established in PSCAD/EMTDC. The simulation results verify the accuracy of the theoretical analysis, as well as the validity of zero-sequence control and MMC topology improvement strategies.
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Enrique, C. Quispe, D. López Iván, J. T. E. Ferreira Fernando, and Sousa Vladimir. "Unbalanced Voltages Impacts on the Energy Performance of Induction Motors." International Journal of Electrical and Computer Engineering (IJECE) 8, no. 3 (2018): 1412–22. https://doi.org/10.11591/ijece.v8i3.pp1412-1422.
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This paper presents the results of a study about the effects of unbalanced voltages on the energy performance of three-phase induction motors. The principal contribution of this paper is that presents a detailed analysis of the influence of positive and negative sequence voltage components and the angle between them on several characteristics such as: line currents, losses, efficiency and power factor under different voltage unbalanced conditions. A three-phase induction motor of 3 HP was used as a case study. The results of the investigation show that the positive sequence voltage must be considered together with the voltage unbalance factor (VUF) or percent voltage unbalance (PVU) index to evaluate the performance of the induction motor. It is also shown that the behavior of the motor load influences on the positive sequence parameters next to the voltage, while in the case of negative sequence only influences the negative sequence voltage.
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Zhang, Jun Li, and Yu Ren Li. "The Simulation Studies of PWM Voltage Source Rectifier under Unbalanced Grid Voltage." Applied Mechanics and Materials 597 (July 2014): 468–71. http://dx.doi.org/10.4028/www.scientific.net/amm.597.468.
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Under the balanced or unbalanced grid voltage, the PWM voltage source rectifiers should have many advantages such as sinusoidal input current, unity power factor, four-quadrant operation, the DC voltage stability, etc., so it can be employed in very broad application field. When there is only fundamental positive sequence current component in AC current, the voltage in DC side will remain constant, the rectifier will achieve efficient transformation of power quality. It is necessary to start from control strategies to eliminate harmful components such as the negative sequence current, to improve power quality in rectifier transformation. The mathematical model of PWM rectifier under unbalanced grid voltage was established in the synchronous rotating coordinate system in this paper. The simulation studies of rectifier under unbalanced grid voltage were conducted
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Huang, Chang Xi, Shu Ying Yang, and Liu Wei Chen. "Unbalanced Control Strategy for DFIG Used in Wind Turbines." Advanced Materials Research 805-806 (September 2013): 430–35. http://dx.doi.org/10.4028/www.scientific.net/amr.805-806.430.
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Unbalanced input voltages would make doubly fed induction generator (DFIG)-based wind turbine operating performance deteriorate, such as shaft tremble, temperature increasing, and so on, even make it cut out of the power grid. Meanwhile, without proper control the power ripples generated from wind turbines may further aggravate power grid. Considering the unbalanced conditions, DFIG was modeled in dual synchronous reference frame (SRF), namely the positive one and the negative one, based on which the dual PI current controllers were designed. To implement the dual current control, the sensing variables were divided into positive and negative sequence components, which were controlled in positive and negative SRF respectively. At the same time, to synchronize with the positive and negative sequence voltage components, a phase latch loop (PLL) control was designed. Experimental results on 11kW DFIG wind turbine test bed validated the designed control system.
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Wang, Xiaosheng, Ke Dai, Xinwen Chen, Xin Zhang, Qi Wu, and Ziwei Dai. "Reactive Power Compensation and Imbalance Suppression by Star-Connected Buck-Type D-CAP." Energies 12, no. 10 (2019): 1914. http://dx.doi.org/10.3390/en12101914.
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Reactive power and negative-sequence current generated by inductive unbalanced load will not only increase line loss, but also cause the malfunction of relay protection devices triggered by a negative-sequence component in the power grid, which threatens the safe operation of the power system, so it is particularly important to compensate reactive power and suppress load imbalance. In this paper, reactive power compensation and imbalance suppression by a three-phase star-connected Buck-type dynamic capacitor (D-CAP) under an inductive unbalanced load are studied. Firstly, the relationship between power factor correction and imbalance suppression in a three-phase three-wire system is discussed, and the principle of D-CAP suppressing load imbalance is analyzed. Next, its compensation ability for negative-sequence currents is determined, which contains theoretical and actual compensation ability. Then an improved control strategy to compensate reactive power and suppress imbalance is proposed. If the load is slightly unbalanced, the D-CAP can completely compensate the reactive power and negative-sequence currents. If the load is heavily unbalanced, the D-CAP can only compensate the positive-sequence reactive power and a part of the negative-sequence currents due to the limit of compensation ability. Finally, a 33 kVar/220 V D-CAP prototype is built and experimental results verify the theoretical analysis and control strategy.
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Hao, Xiaohong, Yangtao Wang, Shuaizheng Sun, Shan Jiang, and Yan Liu. "The Detection Algorithm Based on the Short Time Delay for Three-Phase Unbalanced Voltage Sag." Electronics 11, no. 17 (2022): 2646. http://dx.doi.org/10.3390/electronics11172646.
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To improve the detection speed of the three-phase unbalanced voltage sag, the traditional αβ/dq transformation algorithm can be applied. However, in this algorithm, the virtual quadrature voltage signal (VQVS) needs to be accurately constructed in the αβ coordination system. Then, the information of the voltage jump can be achieved by the αβ/dq transformation. However, the traditional algorithm for constructing the VQVS introduces the harmonic component, so that the detection speed and accuracy is low. To solve the problem, this article modifies the algorithm and presents a new algorithm based on the combination of the short time delay (STD) and the positive- and negative-sequence transformation (PNST) algorithm. The STD algorithm and its construction are firstly detailed. Then, the extraction step and performance of the PNST are given. Since the STD algorithm can avoid harmonic properties, voltage sag signal can be quickly obtained by analyzing the positive and negative sequence component derived from the PNST algorithm. The proposed algorithm is compared with two alternatives already proposed in the literature in terms of detection time. Finally, simulation and experimental results validate the validity of the proposed algorithm.
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Quispe, Enrique C., Iván D. López, Fernando J. T. E. Ferreira, and Vladimir Sousa. "Unbalanced Voltages Impacts on the Energy Performance of Induction Motors." International Journal of Electrical and Computer Engineering (IJECE) 8, no. 3 (2018): 1412. http://dx.doi.org/10.11591/ijece.v8i3.pp1412-1422.
Full textAbstract:
<p class="Abstract">This paper presents the results of a study about the effects of unbalanced voltages on the energy performance of three-phase induction motors. The principal contribution of this paper is that presents a detailed analysis of the influence of positive and negative sequence voltage components and the angle between them on several characteristics such as: line currents, losses, efficiency and power factor under different voltage unbalanced conditions. A three-phase induction motor of 3 HP was used as a case study. The results of the investigation show that the positive sequence voltage must be considered together with the voltage unbalance factor (VUF) or percent voltage unbalance (PVU) index to evaluate the performance of the induction motor. It is also shown that the behavior of the motor load influences on the positive sequence parameters next to the voltage, while in the case of negative sequence only influences the negative sequence voltage.</p>