The Research On The Method Of Transient Stability Analysis Of Wind Power System Considering The Saturation Of Inverter Under VSG Strategy

With the rapid development of micro grid,wind power as one of the most effective and economical way to achieve green environmental protection has been paid a lot of attention at home and abroad.Under the condition that the total capacity of the system is certain,with the increasing of wind power penetration,the proportion of traditional synchronous generators is reduced.Therefore,the total moment of inertia of the system and the spinning reserve capacity will be reduced,which will deteriorate the stability of the system.In order to solve this problem,the expert puts forward the method of using VSG control strategy to simulate the characteristic of traditional generator.However,in the case of large disturbance,similar to the traditional synchronous generator,the inverter with VSG strategy is also appears the problem of instability.Based on the analysis above,the transient stability of wind power system with VSG inverter is studied in this paper.First of all,the principle and mathematical model of VSG control strategy are studied in this paper.The mathematical model of the inverter current saturation is established.According to the current saturation characteristics,the transient characteristics of the inverter virtual angle under the VSG strategy are analyzed.At the same time,the wind power system network model based on VSG strategy is established.The physical equivalence between the inverter and the synchronous generator using the VSG strategy is analyzed.Then,the paper use the traditional transient energy function method to study the stability of wind power system under the VSG strategy.The limitation of the transient energy function analysis method considering the saturation of the inverter is simulated and analyzed.To solve this limitation,starting from the current saturation model,this paper presents an improved method of tangent function approximation,which makes the traditional transient energy function method can correctly analyze the stability of wind power system under the VSG strategy.Finally,the improved transient energy function method based on SMR technology is introduced to improve the conservatism of transient energy function analysis method.In this paper,the principle of SMR technology is studied,and an improved SMR technique is proposed to improve the transient energy function.The improved method is verified by the single machine infinite bus system and three machines system.