# A Short-Circuit Current Calculation Model for Renewable Power Plants Considering Internal Topology
## 1 Introduction  
In recent years, with the large-scale integration of renewable energy into the power grid and the widespread application of high-voltage direct current (HVDC), the power system has been evolving toward a high proportion of power electronics [1], significantly altering the fault characteristics of traditional synchronous machine-dominated grids. When a short-circuit fault occurs in the power system, it is necessary to calculate the SCC for relay protection [2]. Unlike traditional synchronous generators, the SCC of renewable energy, which is integrated via converters, is influenced by control strategies [3; 4]. Research on the SCC of N-SMSs, based on the fault progression, can be divided into transient and steady-state SCC studies. These studies mainly focus on constructing mathematical models of converters, deriving analytical expressions for SCC under different fault conditions, and examining the effects of pre-fault states, low-voltage ride through (LVRT) control strategies, and current-limiting parameters on steady-state SCC. For transient SCC, the control loops of converters are analyzed, and analytical expressions for SCC are derived through system transfer functions or differential equations [5; 6; 7; 8]. Regarding steady-state SCC, control strategies for voltage source converters (VSCs) are introduced, and the impact of current-limiting values on SCC is analyzed [9]. A steady-state SCC calculation model for doubly fed and permanent magnet wind turbines is also developed, considering the effects of LVRT control strategies [10]. Typically, when calculating steady-state SCC, N-SMSs are modeled as voltage-controlled current sources based on LVRT control strategies. At present, research on single-machine SCC for N-SMSs is relatively comprehensive. However, renewable power plants often comprise dozens or even hundreds of N-SMSs, making it impractical to construct detailed models and perform analytical SCCcalculations for each unit during faults. The main method currently used for calculating SCC in renewable power plants is the equivalent method. This study proposes a practical method called the single-machine multiplication method, combined with the traditional SCC calculation approach for synchronous generators, to introduce a local iterative method for the fault region [11]. Although the single-machine multiplication method simplifies the entire renewable power plant into an equivalent non-synchronous machine source, its simplicity comes at the cost of precision, as it neglects the internal variability of the wind turbines in the plant. Hence, accurate equivalent modeling of renewable power plants remains a key challenge. Existing equivalent modeling approaches typically reduce the complexity of renewable power plants based on specific parameters. Wind speed, rotor speed, stator voltage, and real-time active power are selected as clustering indicators, and the doubly fed induction generator is grouped using fuzzy C-means clustering [12]. The fault and fault transition process is discussed, and through the grouping of the active power ramp recovery control module, the photovoltaic power station is subjected to equivalent clustering [13]. One method classifies hybrid wind farms based on turbine types and control strategies [10]. Another method categorizes wind farms according to initial wind speed and steady-state terminal voltage during faults, achieving high accuracy but increasing computational complexity due to iterative calculations of terminal voltage [14]. A further approach analyzes the impact of fault severity and current limiters on active power output, grouping generation units based on the degree of voltage drop, which significantly improves accuracy compared to the single-machine multiplication method [15]. An iterative short-circuit current-voltage algorithm that considers the internal structural parameters of wind farms has been proposed, achieving substantial improvements in convergence, though it increases the number of iterations [16].