Abstract
A power-transmission collection line is connected to each wind turbine of a wind farm and then connected to the incoming switchgear at the low-voltage side of the booster station at a certain distance. Therefore, the grouping of the wind turbines in the wind farm determines the layout of the lines and affects the line impedance. The line structure and composition of the wind farm are analyzed, and the relationship between the impedance of the collection line and reactive power generated by the wind turbine at low-voltage ride through is derived. We conclude that the smaller the equivalent impedance of the wind farm collection line structure is, the greater the reactive power at the wind farm collection line point is. In addition, the economic aspect of the collection line needs to be considered in the design. The economic aspect and impedance values have contrasting characteristics. Therefore, according to the condition of minimum impedance and optimized economic aspect, an optimization model of a wind-farm collector-circuit structure is proposed. The optimal structure of the wind farm collector circuit is calculated using the Monte Carlo method, and the theoretical analysis is verified by simulation.
Highlights
A power-transmission collection line is connected to each wind turbine of a wind farm and connected to the incoming switchgear at the low-voltage side of the booster station at a certain distance
It is concluded that the smaller the equivalent impedance of the wind-farm line structure is, the greater is the reactive power at the collection point in the wind farm, which is more helpful for grid-voltage recovery
According to the theoretical analysis, when the impedance of the current-collection line is smaller, the reactive power at the point where the wind turbine is replenished at the fault point is larger, which contributes to the voltage recovery at the collection point
Summary
Wind energy, as a developing clean-energy source, has driven related industries, continuously promoted the development of national economy, and played a very important role in environmental improvement[1,2,3]. Compared with the doubly fed wind turbines, permanent-magnet direct drives eliminate the need for gearboxes They offer the advantages of high power-generation efficiency, high reliability, low operating and maintenance costs[5]. To study the relationship between the wind-farm collection line and LVRT characteristics, this work establishes the equivalent mathematical model of a wind farm according to its actual construction conditions, including the wind-turbine connection mode, wind-turbine layout, and wire types. It is concluded that the smaller the equivalent impedance of the wind-farm line structure is, the greater is the reactive power at the collection point in the wind farm, which is more helpful for grid-voltage recovery According to this mathematical model, this study mainly investigates the optimization of the layout of the collection line under a grid-voltage symmetrical fault to realize minimum impedance and optimize the economic factor. The Monte Carlo method[11,12] is used to calculate the optimal line grouping, and the optimization method of the wind-farm collection-line structure that considers the economy and LVRT capability is obtained, which has certain practical significance
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