Dimension-Reduction Method and Influencing Factor Analysis for Unit Clusters in Centralized Renewable Energy Stations Considering Short-Circuit Current Fitting Characteristics

The large-scale integration of inverter-interfaced renewable generation has made the steady-state short-circuit current of renewable energy stations increasingly important for setting protections, planning, and fault analysis. Traditional single-unit multiplication methods are computationally efficient but often ignore the effects of internal electrical distance and active power output dispersion among generation units, which can lead to non-negligible errors at the station level. To address this issue, this paper proposes an improved single-unit multiplication method and a corresponding dimension-reduction framework for centralized renewable energy stations considering short-circuit current fitting characteristics. A unified three-segment positive-sequence current control model is first adopted to represent the low-voltage ride-through behavior of photovoltaic (PV), direct-drive wind turbine, and battery energy storage system (BESS) stations. The upper and lower voltage breakpoints are selected as 0.9 p.u. and 0.2 p.u., respectively, and the linear support coefficient was determined as 1.5 according to Chinese national standards. On this basis, the effects of electrical distance and active power output dispersion on the calculation error of the traditional single-unit multiplication method are analyzed. A grouping criterion based on the average access-point voltage and critical active power is then established, and the resulting two-group equivalent method is used to estimate the total short-circuit current of renewable energy stations. Electromagnetic transient simulations in PSCAD are conducted for PV, direct-drive wind, and BESS stations. The results show that, compared with the traditional single-unit multiplication method, the proposed method more accurately captures the steady-state short-circuit current characteristics under different voltage dips and output-dispersion conditions while retaining high engineering practicality.