Research on modelling and simulation of converters for electromagnetic transient simulation in photovoltaic power generation system

Large-scale photovoltaic (PV) power plants connected to the grid leads to the complex calculations in the modelling and simulation of the power system, especially in the electromagnetic transient progress. Common averaging methods are studied for modelling a grid-connected converter to simplify the calculation and balance accuracy and efficiency in simulation. The piecewise technique, which combines the time segment with similar operating characteristic, is applied to different averaging models of converters. The advantages and disadvantages of different piecewise averaging models are compared. In addition, a new piecewise generalised state-space averaging (P-GSSA) model is derived and a multiple time scale modelling is achieved for the grid-connected converters in PV systems. The model error and accuracy of the P-GSSA model are analysed, the physical significance and the influence factors in the model error of P-GSSA model are discussed. The research shows that P-GSSA model is flexible to be used in a PVs system simulation, and it can accurately reflect the steady state and transient characteristics of a converter. The analysis of the P-GSSA model is verified by simulating a DC/AC converter and a PV system.