Equivalent Inertia Evaluation Of Asynchronous Motor And Its Effect On System Frequency Characteristic

With the construction of new power system,the traditional synchronous generator sets have been gradually replaced by wind power and photovoltaic without inertia characteristics,resulting in lower inertia level of the power system,weakened system frequency regulation,and large power outage accidents are more likely to occur,which has become one of the key problems of the current power system that needs to be solved.In addition to synchronous generator inertia,the role of asynchronous motor inertia,which accounts for a high proportion of the load side,on system frequency stability has not been fully investigated.To this end,this paper first establishes an asynchronous motor model based on the potential after transient reactance,then derives the asynchronous motor equivalent inertia by small signal modeling,and finally conducts a series of theoretical verification and simulation studies on the asynchronous motor equivalent inertia.The main work of the article is as follows.1、 Based on the third-order model,the concept of the potential after transient reactance is introduced to establish the asynchronous motor model based on the potential after transient reactance,analyze its asynchronous motor frequency response process when the grid frequency is disturbed,and compare and analyze it with the traditional asynchronous motor detailed model for simulation,verify the correctness of asynchronous motor model based on the potential after transient reactance.2、 On the basis of asynchronous motor model based on potential after transient reactance,the expression of asynchronous motor equivalent inertia is further derived through the analysis method of small-signal modeling.Through the response mechanism analysis,it is found that asynchronous motor equivalent inertia presents time-varying characteristics under the joint action of slip frequency and rotor speed.Then asynchronous motor equivalent inertia is compared with the evaluation methods in the existing literature to verify the correctness of asynchronous motor equivalent inertia.3、 On the basis of asynchronous motor equivalent inertia,the effect of asynchronous motor equivalent inertia on the system frequency characteristics is theoretically calculated and analyzed through system frequency response model from multiple perspectives.Then,through a series of simulation verification,the results show that asynchronous motor equivalent inertia can essentially improve the system frequency stability.Moreover,the error direction when asynchronous motor equivalent inertia is ignored is clearly pointed out.The comparison between simulation and theoretical verification shows that the two analysis results are basically consistent,which proves the effectiveness and feasibility of asynchronous motor equivalent inertia proposed in this paper.