Research On Comprehensive Evaluation Method And Dynamic Optimized Compensation Strategy Of Voltage Sag

Voltage sag has become the most serious power quality problem in modern power grids.It is necessary to study its evaluation techniques and countermeasures for power grids and users.Combined with the sag tolerance characteristics of sensitive equipment,the customized severance severity assessment and compensation strategy formulation can make the sag assessment and compensation refined.Based on the sag tolerance characteristics of sensitive equipment,this paper studies the three aspects of node voltage sag tolerance characteristics,sag severity assessment method and dynamic voltage restorer compensation control strategy.The description method of node voltage sag tolerance characteristics,sag severity assessment method and compensation strategy of dynamic voltage restorer are studied in this paper.First,the description of the current common voltage tolerance curves of sensitive equipment are analyzed,and a description method of node voltage sag tolerance characteristics is proposed.By extracting the most sensitive curve and least sensitive curve of the typical sensitive equipment voltage tolerance curves connected by the node,the uncertainty region of the node voltage tolerance curve is formed.According to the distribution characteristics of the voltage tolerance curve of each sensitive equipment,the uncertainty region is further divided into three sub-regions,which in turn form the final description of the node voltage sag tolerance characteristics.In practical applications,taking into account the difficulties of obtaining the type of sensitive equipment and their voltage tolerance curves,an approximate description of the node voltage sag tolerance characteristics is given,considering the four most typical sensitive devices,such as adjustable speed drives,AC contactors,PCs,and programmable logic controls.Next,the severity of the voltage sag is respectively evaluated from the system side and the load side.For the system side,this paper proposes an extenics evaluation model of the severity of voltage sag is proposed in this paper.Considering the four characteristic quantities of magnitude,duration,point-on-wave and phase angle jump and dividing the interval,the voltage sag severity level of a single event is obtained.Furthermore,according to the distribution of the evaluation results of all the sag events of the node at each level,the node voltage sag severity level is finally obtained.Aiming at the non-rectangular phenomenon of voltage tolerance curve of sensitive equipment,a description form of linearization processing is presented,and an evaluation model based on the principle of energy loss is established,which can more accurately evaluate the impact of voltage sag on sensitive equipment.On this basis,an assessment method for evaluating the sag impact on industrial production process is proposed,considering the connection method of each equipment,which can calculate the probability of industrial process interruption caused by voltage sag.Through the example analysis,the rationality of the system side and equipment side voltage sag evaluation methods proposed in this paper is verified.Finally,considering the power supply mode and voltage sag tolerance of the sensitive load and the capacity limitation of dynamic voltage recovery,a voltage sag dynamic optimized compensation strategy of dynamic voltage recovery is proposed.Compared with the traditional compensation strategy,the strategy proposed in this paper ensures the normal operation of the sensitive load,the energy loss in the compensation process can be greatly reduced,and the compensation capability of dynamic voltage recovery can be improved.The simulation based on Matlab/Simulink verifies the effectiveness of the dynamic optimizated compensation strategy proposed in this paper.