| With the continuous improvement of photovoltaic installed capacity,power fluctuations during the operation of photovoltaic inverters and the problems of power quality caused by it have attracted widespread attention,especially when the grid has experienced voltage sag,which will have a great impact on photovoltaic inverter operation.At the same time,the photovoltaic inverter will also affect the power quality of the grid connection point when voltage sag.Therefore,it is necessary to master the voltage sag tolerance characteristics of photovoltaic inverters and study their low voltage ride-through control strategies.First,analyze the typical topology of a photovoltaic inverter to determine the topology studied in this paper.The mathematical model in the three-phase ABC coordinate system is analyzed for the researched topology,and in order to facilitate the set up of the control strategy described below,the positive and negative sequence dq-axis rotating coordinate system and αβ two-phase stationary mathematical model in the coordinate system of the photovoltaic inverter under the unbalanced voltage sag is analyzed;on this basis,the influence of the voltage sag on the photovoltaic inverter is analyzed.Secondly,a photovoltaic inverter model was built on the PSCAD/EMTDC platform to analyze the voltage sag tolerance characteristics and power output characteristics.According to the impact mechanism of photovoltaic inverter voltage sag,the influence of factors such as sag start point,sag type,imbalance,light intensity,and DC-side capacitance on the photovoltaic inverter sag tolerance curve are studied in order,and the research The effects of multiple sags and continuous sags on the tolerance of photovoltaic inverters are described.In addition,the power sag output power curves of photovoltaic inverters under different types are analyzed,and the power output characteristic curves of photovoltaic inverters under different sag types are obtained.Then,in order to suppress the peak current when the unbalanced voltage sag occurs in the power grid,and consider reducing the active power and reactive power fluctuations of the PV inverter output during unbalanced sag,current imbalance.Multi-objective photovoltaic inverter control strategy considering current peak under voltage sag is proposed.Aiming at the problem of voltage support of photovoltaic inverter during voltage sag,and considering the suppression of power fluctuation and current distortion of photovoltaic inverter during unbalanced voltage sag,an improved transient considering voltage support under unbalanced voltage sag is proposed.Active and reactive photovoltaic inverter control strategy.A photovoltaic simulation model was built on the PSCAD/EMTDC platform to verify the effectiveness of the proposed two control strategies,which is consistent with the theoretical analysis. |
