Analysis Of Load Characteristics Of Induction Motors Considering Frequency Changes And Their Effects On Transient Voltage Stability

With the gradual development and improvement of China's strategic project of “West-East Electricity Transmission,North-South Interconnection,and National Networking”,China Southern Power Grid has become one of the most complex networks in the world.The mode of interconnected operation puts forward new requirements for the accuracy of power system simulation analysis.The impact of load model on the stability calculation results of networked systems cannot be ignored.When modeling the power system,considering the voltage characteristics and frequency characteristics of the load model,it can more realistically reflect the load dynamic characteristics of the actual system.From the perspective of modeling,induction motors,as the main electrical load,belong to the category of load modeling.Whether the induction motor is in good operating condition has become an important factor affecting the continuity of industrial production.In view of the above contents,this paper takes the induction motor as the research object,and studies its voltage characteristic and frequency characteristic.In addition,the transient voltage stability of induction motor with frequency variation is studied in depth on the basis of verifying the influence of system frequency variation on the absorbed power of induction motor.The main research contents of this paper are as follows:Analysis of load characteristics of induction motors with different load types.According to the induction motor ? type equivalent circuit,using the analytic method is derived under steady state and dynamic process,different load types of induction motor slip,electromagnetic torque and mechanical torque,absorption of active power and reactive power with the relational expression of system frequency or voltage change.Finally,the frequency characteristic coefficient and voltage characteristic coefficient of the induction motor are calculated.MATLAB/SIMULINK software was used to build the dynamic load model of the power system,and the influence of frequency and voltage disturbance on the load characteristics of the induction motor was simulated to verify the correctness and effectiveness of the theoretical derivation.Analysis of the influence of different parameters of induction motor on load characteristics.The stator inductance,rotor inductance,magnetic inductance,rotor resistance,the moment of inertia and other parameters of the induction motor are changed respectively.Within the credible variation range of each parameter,the frequency characteristic coefficient and voltage characteristic coefficient of the induction motor under different parameters are calculated theoretically.Analyze the effect of different parameters on the load characteristics of the induction motor.The MATLAB/SIMULINK software was used to simulate and analyze the load characteristics of induction motors under different parameters to verify the correctness of theoretical derivation.Research on the analytical algorithm of the symmetrical voltage drop critical clearing time of induction motor with frequency variation.Aiming at the most serious symmetrical voltage drop in the power system,taking into account the influence of frequency variation,the analytical expression of the critical clearing time of the symmetrical voltage drop of the induction motor with different load characteristics is derived.Taking the constant mechanical torque-induction motor as an example,the theoretical results of the analytical algorithm are verified by a large number of experiments.The effect of changes in the parameters of the induction motor taking into account the change in frequency on the critical clearing time of the transient voltage.Taking the constant mechanical torque induction motor with frequency variation as an example,the parameters of the induction motor,such as stator and rotor resistance,stator and rotor inductance,excitation inductance,and moment of inertia,are changed.The critical clearance time of transient voltage stability is calculated by analytical algorithm and the influence of internal parameters on transient voltage stability is analyzed.Simulation results are obtained through a large number of trial and error experiments,which verify the effectiveness and accuracy of the analytical algorithm.