Modelling and simulation of the solar photovoltaic systems for grid studies considering the negative sequence control strategy

One of the main trends in the development of solar photovoltaic (PV) grid-connected technology is the in-depth study of modelling the PV system and simulation for the transient characteristics. But the commonly used dynamic models are not available for the electromechanical transient (RMS) unbalance simulation. This paper presents an improved model which is based on the GE solar plant model for asymmetric fault. Firstly, It derives the differential equations correspond with the equivalent circuits of the PV system and extends the frame of the model which can contain the positive negative and zero sequence (PNZ-seq.) network. The converter block is redesigned to provide an interface between the PV system and the multiphase (balanced or unbalanced) network. Then, it emphasis on the control block which dictates the active and reactive power to be delivered based on command. The innovative improvement is to consider the P-Seq. and N-Seq. coordination control strategy for RMS unbalance simulation. Finally, the improved model is implemented in the DIgSILENT PowerFactory software. The simulation results have illustrated that the improved model can more accurately reflect the transient characteristics and contribute to a more accurate stability analysis of large PV system connected to the grid.