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Harmonic amplification and interaction of the PV plant which contains multiple parallel inverters influence the renewable power generation and operation seriously. In this article, the resonance mechanism and characteristics of a real large-scale PV plant are explored based on its plant-level circuit model. The component and system models are established first. The distribution rules of wideband resonance frequency from the perspective of the point of common coupling (PCC) and the inverter are respectively determined. Two different resonance bands excited by LCL filter and underground cable are further identified. At last, the practical case of harmonic resonance in the studied PV plant is investigated. Both the measured data and the simulation results support the analytical conclusions. This article combines the theoretical study with the engineering practice, which provides beneficial guidance on the resonance prevention. [ABSTRACT FROM AUTHOR]

The rapid development of modern vessel leads to higher demands on the optimization and integration of shipboard power supply system (SPSS). In this article, a compact-design oriented 12-pulse parallel operating transformer employing shared integrated filter is presented for power quality improvement of SPSS with reduced installation space. The proposed SPSS is featured with harmonic-free power supply and high integration of power equipment. The system topology is introduced first, and the distinctive compensation principle is then analyzed. Taking into account both of the winding impedance matching and transformer size optimization, minimum radial dimension is searched and determined in the interval of approximative zero-impedance. Moreover, the inductance calculation method of integrated reactor together with its design domain is further given out. At last, the prototype of the proposed SPSS is tested in laboratory. The experimental results verify the feasibility and effectiveness of the proposal. [ABSTRACT FROM AUTHOR]

In this article, a new harmonic mitigation system using double balanced impedance filtering power transformer (DBI-FPT) is proposed for improving the power quality (PQ). Designed for multistage distribution network with severe harmonic pollution, the proposed system enhances multiport filtering performance, mitigates resonance along with reduction of construction and maintenance costs compared to other alternative system. The simplified model of the proposed system is established by combining the short-circuit impedance calculation method and the characteristics of dual-balanced winding. By analyzing the influence of manufacturing errors on the dual-balanced winding in detail, the optimization method for filtering performance is given, which in turn guides the practical application of DBI-FPT effectively. After that, through comprehensively comparative analysis, the multiport harmonic mitigation characteristics, resonance avoidance, and amplification weaken mechanism of the proposed method are revealed. The experimental results validate that the proposed system is suitable for multiterminal PQ improvement and industrial application in multistage regional distribution network. [ABSTRACT FROM AUTHOR]

This article proposes an inductive filtering-based parallel operating transformer with a shared filter to improve the power quality at the grid-connected step-up station of a wind farm. Only a set of the shared inductive filter is configured to serve for two wind farms (two harmonic sources). The proposed transformer together with the shared filter has the merits of less installation space, higher equipment utilization, and better filtering performance compared with the conventional scheme. The three-phase mathematical model of the step-up station is established. Its simplifying circuit is obtained considering the symmetry and asymmetry parameters of the transformer impedance. The filtering mechanism, operating characteristics, and the realization condition of satisfactory filtering performance are further revealed. At last, the proposal is verified to be feasible and effective by means of simulation results and field measurements. [ABSTRACT FROM AUTHOR]

This paper proposes a transformer integrated filtering system (TIFS) for harmonic suppression in the industrial dc supply system. Designed for the electric environment with large current and severe harmonic contamination and the installation space with restricted planning area, the proposed TIFS has the merits of lower transformer loss, stronger ability in harmonic elimination, and higher integration of the electric equipment in the high-power industrial applications. The winding arrangement of the inductive filtering transformer with integrated reactor is introduced. Considering the influence of the residual weak coupling, the electromagnetic decoupling model of TIFS is established. Then, the interaction between the zero-impedance designed filtering winding and the decoupled winding is analyzed to determine the restricted range of the design parameter. The control strategy together with the transformer design method is further illuminated. At last, the prototype of TIFS is established in the laboratory. The experimental results verify the feasibility and effectiveness of the proposed filtering method. [ABSTRACT FROM AUTHOR]

This paper presents a new solution of power quality management for the photovoltaic (PV) power plant with the transformer integrated filtering method. The innovation of the PV power plant is that it contains two-stage filtering station, which consists of a box-type transformer with integrated filter and a 110 kV grid-connected transformer based on inductive filtering method. The filtering reactor can be integrated into the box-type transformer as a decoupled winding, so that the modular design of the box-type transformer and the passive filter is realized. Inductive filtering method applied in the grid-connected transformer not only improves the power quality at the point of common coupling, but dampens the harmonic resonance between the passive filter and grid. The hierarchical structure of the PV power plant is introduced firstly. Then, the equivalent circuit model and the mathematical model of the primary and secondary filtering stations are established, respectively. Moreover, the influence of the weak coupling of integrated reactor on the filtering performance is analyzed. The antijamming capabilities of the inductive filtering method and the traditional filtering method are compared under the condition of parameter disturbance. At last, the site tests of the PV power plant with transformer integrated filtering method are made, which show that the PV grid-connected system comprised of the two-stage filtering station has the characteristics of low harmonic emission, high power factor, and stable operation. [ABSTRACT FROM AUTHOR]

Highlights • Establishing the three-phase equivalent mathematical model for CIPF. • Revealing the distinctive operational mechanism of the CIPF method in a mathematical sense. • Finding out the operational law. An improved control strategy is designed. Abstract This paper presents a controllable inductive power filtering (CIPF) system with the novel filtering mechanism. Due to the zero-impedance design of the power transformer, the harmonic magnetic flux between the secondary load winding and the customized filtering winding can be balanced each other. Hence, the contaminated area of harmonics is reduced. The addition of the active filter contributes to further improve the filtering performance with the task of harmonic isolation between the power grid and the load. First, the three-phase unified equivalent circuit model and the mathematical model are given out at the harmonic domain. Based on the deduced transfer matrix, the filtering evaluation criterion of CIPF system is established, and the filtering principle is revealed, as well. According to the special operational law, an improved virtual impedance control strategy is designed to prevent the potential harmonic amplification, and the relationship between the phase/magnitude of the virtual impedance and the filtering performance is discussed. Finally, the experimental results based on the laboratory scaled prototype show the validity of the CIPF system with improved virtual impedance control. [ABSTRACT FROM AUTHOR]