Abstract
Short-circuit current level of power grid will be increased with high penetration of VSC-based renewable energy, and a strong coupling between transient fault process and control strategy will change the fault features. The full current expression of VSC-based renewable energy was obtained according to transient characteristics of short-circuit current. Furtherly, by analyzing the closed-loop transfer function model of controller and current source characteristics presented in steady state during a fault, equivalent circuits of VSC-based renewable energy of fault transient state and steady state were proposed, respectively. Then the correctness of the theory was verified by experimental tests. In addition, for power grid with VSC-based renewable energy, superposition theorem was used to calculate AC component and DC component of short-circuit current, respectively, then the peak value of short-circuit current was evaluated effectively. The calculated results could be used for grid planning and design, short-circuit current management as well as adjustment of relay protection. Based on comparing calculation and simulation results of 6-node 500 kV Huainan power grid and 35-node 220 kV Huaisu power grid, the effectiveness of the proposed method was verified.
Highlights
Grid-connected power generation scale of renewable energy sources, like wind energy and solar energy, is continuously expanding, and renewable energy sources connected to grid with high penetration will become an important trend of future electric power system [1,2,3,4]
With higher penetration of renewable energy power generation in electric power system, short-circuit currents injected by them during short-circuit fault will increase current at fault point, and electrical equipment are faced with higher requirements for dynamic and thermal stability [5]
Short-circuit current calculation of power grid with a high penetration of renewable energy sources are basic for the electric power system planning and design, equipment selection, and protection configuration
Summary
Grid-connected power generation scale of renewable energy sources, like wind energy and solar energy, is continuously expanding, and renewable energy sources connected to grid with high penetration will become an important trend of future electric power system [1,2,3,4]. The peak value of short-circuit current for electric rotating machinery is very high, while that is limited for VSC-based renewable energy due to its control strategy of converter. It can be divided into voltage-control and current-control converter according to difference in controlled inner loops [14]. In aspect of short-circuit current calculation, based on the method of equivalent generator voltage at the fault location, an algorithm principle is proposed to calculate short-circuit current in distribution networks, but control and current-limiting features of VSC-based renewable energy were not considered in [22]. Huaisugrids and Huainan power grids are with high penetration of VSC-based renewable energy
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