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.

The probabilistic short-circuit current (PSCC) of photovoltaic generation is determined by the voltage sag at the grid connection and the low voltage ride-through of the unit during the grid fault, while the voltage sag and the low voltage ride-through are both stochastic. According to short-circuit current characteristics and Thevenin equivalent circuit in the transient state, this paper analyzes the changing trajectory of the equivalent internal potential of photovoltaic generation during the period of low voltage ride-through. To deal with the uncertainty of low voltage ride-through, the probability density function by the maximum entropy method is used to characterize the stochastic process of low voltage disconnection of photovoltaic generation. Based on the fault information, the calculation method of PSCC in active distribution network considering the uncertainty of low voltage ride-through of photovoltaic generation is proposed. Two cases of 9-node and 34-node distribution network are used to verify the effectiveness of the method. The obtained PSCC results can reasonably reflect the actual short-circuit current level of the active distribution network.INDEX TERMS Photovoltaic, probabilistic short-circuit current, low voltage ride-through, active distribution network.

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A large number of photovoltaic power sources connected to the grid will increase short-circuit current level of power system, and its fault transient process will change the fault characteristics of power grid. In this paper, the equivalent models of transient and steady state faults are obtained, by analysing the full current expression of photovoltaic power sources and its current characteristics in different fault stages. Based on the superposition theorem, the short-circuit current calculation method of power system with photovoltaic power sources is proposed. Finally, the effectiveness of the proposed method is verified by the analysis of actual power grid calculation examples, and the results can be used for power grid planning and relay protection setting.