Abstract
Neutral grounding through resistance is widely applied in large-scale centralized grid-connected photovoltaic power stations (PVPS), while protection measures, which are supposed to cut off the single-phase grounding fault of the collection system quickly, are required according to the grid code. Analyses on the coordination between protection performances and low voltage ride through (LVRT) are missing in current researches. Hence there could be a risk that large-scale photovoltaic units may disconnect from the grid as a result of a mismatch between the protection and LVRT. In view of the above, this paper makes contributions in two aspects. Firstly, this paper proposes a scheme on neutral point resistance selection, which is to analyze the influences on protection performances by the fault characteristics of the single-phase grounding fault of the PVPS collection system in different test environments, and then to quantify the speed and the selectivity of the zero-sequence current protection performance as assessment indexes, as required in the coordination between protection performances and LVRT, and in the coordination between protection performances of tie lines and collector lines of the collection system, and finally to select neutral point resistance based on the indexes. Secondly, this paper proposes a comprehensive control strategy on the large-scale PVPS, which can effectively improve the assessment indexes mentioned above of the protection under different active power production scenarios. Finally, a simulation will be conducted to verify the correctness and the feasibility of the resistance selection scheme and the control strategy proposed in this paper.
Highlights
Concepts such as energy transition, reliable energy supply, sustainable energy resources, and low environmental footprint are central to current research [1]
EVALUATION INDEX OF PROTECTION PERFORMANCE AND RESISTANCE SELECTION Based on the analysis of the above-mentioned fault characteristics, two indexes for evaluating the performance of the zero-sequence current protection are proposed: 1) SPEED INDEX In order to meet the requirements of low voltage ride through (LVRT) for no-fault collector lines on the same bus, the sensitivity index of instantaneous-trip protection (ITP) considering speed, minimum range lmin, is proposed, so that all the fault locations on the tie-line, which leads the Point of Common Coupling (PCC) voltage is less than 0.2 times the rated value, should be included in lmin during a single phase-to-ground fault
Static var generator (SVG) are usually installed in large-scale PV power stations to compensate for reactive power losses on transformers and lines in the station, and provide reactive power to support the bus voltage during failure, which is one of the important differences between large-scale centralized grid-connected PVPS and distributed PV generator
Summary
Concepts such as energy transition, reliable energy supply, sustainable energy resources, and low environmental footprint are central to current research [1]. Another one of the stringent requirements in GC is the low voltage ride-through [8], [9], needed to avoid sudden tripping of PV generation due to grid faults. Different neutral point grounding methods lead to different treatment methods for single-phase ground faults [24], second, the PVPS collection system includes convergence bus and collector lines, and each collector line contains multiple PV units, so the protection performance of PVPS needs to meet the two dimensional coordination requirements at the same time.
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