Research On Fuzzy Criterion Of Distinguishing The Angle Stability And Voltage Stability

Since the 1920 s,the power system stability has caused the attention of researchers and is regarded as an important aspect of the safe and reliable operation of the power system.System stability modes mainly include the angle stability,voltage stability and frequency stability.Different stability problems have different characteristics and basic principles,and reflect different main problems,and the corresponding subsequent transient stability control measures are also different,so it needs to determine more accurate instability mode in practical analysis.The principle of frequency problem is simple and easy to be identified,but the angle stability and voltage stability are more complex and they often intertwine.The angle instability may cause the voltage instability and voltage instability may also lead to the angle instability,so it is difficult to distinguish angle instability from voltage instability according to the change of angle and voltage in the process of instability.Therefore,seeking a method that can distinguish different instability modes according to the change information of system electric parameters is particularly important.Based on the existing research on definition of voltage stability and angle stability and the connection and influence with each other,this paper built a set of indexes reflecting instability characteristics,starting from the basic principle of angle stability and voltage stability,combining the changing rule related of characteristic variable of generator,tie link and load from the angle to the voltage problems in the transition process.These indexes include the generator relative speed,accelerate energy,load voltage level,reactive power changing rate of generator and load and line power factor index.From the change information of these indicators,we can find out the law of the change of the system instability mode,so as to distinguish them effectively.Combined with the basic principle of fuzzy theory,the membership function of each index can be obtained by assignment method and the subjective weight can be calculated by sequence relationship analysis,and then the comprehensive fuzzy function was established.On this basis,a fuzzy criterion between 0 and 1 was got combining the small system case of two generators to fuzzily evaluate the degree of instability of different instability modes.In the end,an actual power grid case was used to verify the effectiveness of the criterion.