The Experts below are selected from a list of 109608 Experts worldwide ranked by ideXlab platform
Wu Jian - One of the best experts on this subject based on the ideXlab platform.
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A Method to Compute Voltage Unbalance Factor in Three-Phase Three-Wire System
Power system technology, 2010Co-Authors: Wu JianAbstract:Three-phase voltage unbalance factor is one of the important indices in the measurement of power quality. Under the power supply by three-phase three-wire power system, the accuracy, merits and drawbacks of current methods to calculate three-phase voltage unbalance factor are compared and analyzed, and a new method to calculate voltage unbalance factor suitable to three-phase three-wire power system is proposed. Needing not complex vector computation and only using the voltage amplitudes of three phases, the proposed method can accurately calculate positive-Sequence Component, negative-Sequence Component and three-phase unbalance factor. Detailed formula derivation is given, and calculation results of a lot of living examples show that the proposed method is correct.
Gao Jun - One of the best experts on this subject based on the ideXlab platform.
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A novel dynamic voltage restorer and its unbalanced control strategy based on space vector PWM
International Journal of Electrical Power & Energy Systems, 2002Co-Authors: Hongfa Ding, Shu Shuangyan, Duan Xianzhong, Gao JunAbstract:A novel dynamic voltage restorer which is composed of a conventional three-phase voltage source inverter and an emitter follower is presented in this paper to reduce the adverse effects on sensitive loads caused by three-phase supply voltage unbalance in distribution systems. The adverse effect caused by the negative Sequence Component of the supply voltage can be eliminated and the load voltage magnitude can be restored to specified value by using the three-phase voltage-source inverter. The emitter follower is capable of eliminating the adverse effect caused by the zero Sequence Component of the supply voltage. An unbalanced control strategy based on space vector PWM is presented to realize the fast dynamic response of the dynamic voltage restorer. Feasibility of this method is verified by digital simulation.
Mehrdad Kazerani - One of the best experts on this subject based on the ideXlab platform.
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A Sequence-Component-Based Power-Flow Analysis for Unbalanced Droop-Controlled Hybrid AC/DC Microgrids
IEEE Transactions on Sustainable Energy, 2019Co-Authors: Mahmoud A. Allam, Am A. Hamad, Mehrdad KazeraniAbstract:This paper proposes a generalized and efficient power-flow algorithm for islanded hybrid ac/dc microgrids. The algorithm considers the microgrid operational aspects, i.e., absence of a slack bus, unbalanced ac subgrid, droop-controlled ac and dc voltages and ac frequency, and coupling between the ac frequency and dc voltage through interlinking converters. To attain high computational efficiency, the algorithm adopts three features. First, it models the ac subgrid elements in Sequence Components, thereby dividing the subgrid's set of equations into three smaller sets for faster parallel solution. This approach also accurately represents the different types of ac distributed generators. Second, the algorithm sequentially solves for the power-flow variables of the ac and dc subgrids, thus reducing the number of equations to be solved simultaneously, once again for further computational cost alleviation. Third, the algorithm implements the quadratically convergent Newton-Raphson technique to solve the decoupled sets of equations. The proposed algorithm is validated through comparisons with time-domain simulations, in MATLAB/Simulink, for test hybrid ac/dc microgrids of different configurations. Moreover, three case studies are introduced to examine the proposed algorithm's effectiveness in solving large-scale microgrids, to investigate its limits-enforcement capabilities, and to evaluate its performance as compared to conventional methods.
Kazerani Mehrdad - One of the best experts on this subject based on the ideXlab platform.
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A Sequence-Component-based power-flow analysis for unbalanced droop-controlled hybrid AC/DC microgrids
IEEE, 2018Co-Authors: Allam, Mahmoud A., Said Amr, Kazerani MehrdadAbstract:This paper proposes a generalized and efficient power-flow algorithm for islanded hybrid ac/dc microgrids. The algorithm considers the microgrid operational aspects, i.e., absence of a slack bus, unbalanced ac subgrid, droop-controlled ac and dc voltages and ac frequency, and coupling between the ac frequency and dc voltage through interlinking converters (ICs). To attain high computational efficiency, the algorithm adopts three features. First, it models the ac subgrid elements in Sequence Components, thereby dividing the subgrid's set of equations into three smaller sets for faster parallel solution. This approach also accurately represents the different types of ac distributed generators (DGs). Second, the algorithm sequentially solves for the power-flow variables of the ac and dc subgrids, thus reducing number of equations to be solved simultaneously, once again for further computational cost alleviation. Third, the algorithm implements the quadratically-convergent Newton-Raphson technique to solve the decoupled sets of equations. The proposed algorithm is validated through comparisons with time-domain simulations, in MATLAB/Simulink, for test hybrid ac/dc microgrids of different configurations. Moreover, three case studies are introduced to examine the proposed algorithm's effectiveness in solving large-scale microgrids, to investigate its limits-enforcement capabilities, and to evaluate its performance as compared to conventional methods.Peer reviewed: YesNRC publication: Ye
Jul-ki Seok - One of the best experts on this subject based on the ideXlab platform.
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Correction on Current Measurement Errors for Accurate Flux Estimation of AC Drives
2016Co-Authors: At Low Stator Frequency, Kyung-rae Cho, Student Member, Jul-ki SeokAbstract:Abstract—This paper presents an online-correction method for current measurement errors for a pure-integration-based flux estimation down to a stator frequency of 1 Hz. A measurement-disturbance-observer (MDO)-based approach is taken as one pos-sible solution for eliminating the dc offset and the additional negative-Sequence Component due to unbalanced current mea-surement gains in the synchronous coordinate. From the motor parameter sensitivity analysis, an MDO gain selection method is proposed to remove the estimation error resulting from a parame-ter mismatch. At the same time, the positive-Sequence Component estimation is performed by creating an error signal between a motor model reference and an estimated q-axis rotor flux estab-lished by a permanent magnet in the synchronous coordinate. The compensator utilizes a PI controller that controls the error signal to zero. Experimental results confirm that the proposed scheme has great potential for applications to acquire the accurate motor flux at a low stator frequency. Index Terms—DC offset, measurement disturbance observer (MDO), negative-Sequence Component due to unbalanced current measurement gains, online-correction method of current mea-surement errors, positive-Sequence Component estimation, pure-integration-based flux estimation. I
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Control of series active power filters compensating for source voltage unbalance and current harmonics
IEEE Transactions on Industrial Electronics, 2004Co-Authors: G-myoung Lee, Dong-choon Lee, Jul-ki SeokAbstract:In this paper, a novel control scheme compensating for source voltage unbalance and current harmonics in series-type active power filter systems combined with shunt passive filters is proposed, which focuses on reducing the delay time effect required to generate the reference voltage. Using digital all-pass filters, the positive voltage Sequence Component out of the unbalanced source voltage is derived. The all-pass filter can give a desired phase shift and no magnitude reduction, unlike conventional low-or high-pass filters. Based on this positive-Sequence Component, the source phase angle and the reference voltage for compensation are derived. This method is easier to implement and to tune controller gains. In order to reduce the delay time effect in the voltage control loop, the reference voltage is predicted a sampling period ahead. The validity of the proposed control scheme has been verified by experimental results.
