The invention provides an aggregation equivalent method for a large-scale 
photovoltaic power generation system based on a structure preserving method. The method comprises the steps of establishing adetailed 
mathematical model of a two-stage 
photovoltaic power generation system, wherein the detailed 
mathematical model comprises a 
mathematical model of a photovoltaic array, an average model of a preceding-stage Boost circuit, an average model of a backward-stage grid-connected 
inverter, an 
equivalent model of a 
transformer, and mathematical models of a 
maximum power point tracking controller and a grid-connected 
voltage and current controller; according to an 
energy conservation relation among 
magnetic field energy, 
electric field energy and generalized 
potential energy existing in the 
photovoltaic power generation system, obtaining a relation between state variables the detailed model and an 
equivalent model of the large-scale photovoltaic 
power generation system; determining a current and 
voltage relation between the detailed model and the 
equivalent model according to the same active 
power output and 
power grid access mode between the detailed model and the equivalent model; andutilizing a capacity weighting method, comparing state equations among different models, and providing an equivalent parameter calculation method of an aggregation equivalent model. The method has the beneficial effects that the aggregation model is enabled to reserve the same circuit and control structure as the original photovoltaic 
power generation system on the basis of simplifying the 
reduced order model, and meanwhile, an accurate and reliable calculation method is provided for solving equivalent parameters of a photovoltaic array, a Boost circuit, an 
inverter, an output filter, a 
transformer, a 
maximum power point tracking controller and a grid-connected 
voltage and current controller in the aggregation equivalent model.