Modeling Of Electromechanical Timescale Of Induction Motor Based On Internal Voltage Magnitude-phase Motion Equation And Its Impact On Power System Electromechanical Dynamics

Induction motors are the main load in power systems.Although the variable voltage and variable frequency technique makes part of induction motors connect to power systems with electronics realizing the varied speed performance,large amount of induction motors still directly integrates to power systems for the costs,operation reliability and maintenance.The dynamic characteristics of induction motors have important influence on power system dynamic stability.Therefore,the study of the dynamic characteristics of induction motors and their impacts on power system dynamic stability are important for analyzing,understanding and solving problems.This paper reviews the modeling approaches used in the past for characterisitics description of induction motors and the researches of induction motors' effect on power system stability.It is considered that the characterisitcs of induction motors in the past are described with emphasis either on the mathematical description of their internal components or on the unilateral description of specific issues of specific scenario,which lead to the lack of intuitive physical understanding and comprehensive summary of the effect of induction motors on power systems stability.Therefore,the key to the study is to fully understand the dynamic characterisitcs of induction motors.Based on the concept of voltage magnitude-phase motion equation,this paper describes the dynamic charactersitics of induction motors as the process of coupled active power balancing and reactive power balancing driving the internal voltage magnitude-phase.With the help of dynamics,this modeling approach describes the motion law of internal voltage magnitude and phase state under the action of unbalanced power,which is helpful to physical understanding of the dynamic behavior of induction motors.Combining the induction motors' internal voltage magnitude-phase motion equation,this paper studies the voltage magnitude-phase dynamics in electromechanical timescale and its effects on power system electromechanical timescale stability,which can summarized as follow:1.This paper introduces the basic concept of internal voltage magnitude-phase motion equation and defines the induction motors' internal voltage vector in electromechanical timescale.Then,we propose the motion equation of induction motors in electromechanical timescale and conclude the dynamic performance of internal voltage magnitude-phase driven by unbalanced input active and reactive power under an electromechanical timescale disturbance.In a single induction motor-infinite bus system,we validate the correctness of the proposed model by comparing the detailed model in time-domain simulation.2.Based on the motion of internal voltage magnitude-phase driven by active power balancing and reactive power balancing,this paper studies the short-term voltage stability of a single induction motor-infinite bus system.By analyzing the characteristics of the induction motor itselves,a criterion for large disturbance stability of induction motors with combined active power balance and reactive power balance is proposed.In this paper,we take the stall and low voltage instability as examples,the specific analyses of the above criteria under two kinds of instability condition are given.The time domain simulation verifies the accuracy and rationality of these analyses.3.The dynamic response of induction motors under a frequency disturbance is discussed based on the internal voltage magnitude-phase motion equation.The frequency domain expression of the available inertia is distilled by linearizing the induction motor's internal voltage phase motion equation,and the basic characterisitc of available inertia is analyzed.Combing with the internal voltage phase motion equation,the frequency dynamics in inertial response timescale are studied in a simple system scene of wind power,synchronous generator and induction motors.Simulation results based on time domain verify the accuracy of induction motors' available inertia and its effect on the frequency dynamics of wind power integrated system.4.Based on the essence of active power exchange and reactive power exchange,this paper studies the basic principle of the interaction between induction motors and the terminal voltage control in STATCOM in the case of an induction motor with reactive power compensation equipment incorporated into an infinite system through a long line.The analytical model of the system interaction is established based on the motion equation.The effects of different terminal voltage control methods,grid strength and the inertia constant of induction motors on the interaction are investigated.This paper discusses the applicable parameter ranges of integral controller and proportional-integral controller under terminal voltage control,and provides references for the design of voltage controller parameters of reactive power compensation equipment under different grid strengths.