| As the application of sensitive electrical equipment,such as computer system,automatic production line,programmable logic controller in industrial production,users have put forward higher requirements for the quality of electric energy.However,the large-scale access of renewable energy,the wide application of power electronic equipment,the operating of electrified locomotives and high-capacity impact loads and nonlinear loads have caused serious interference and pollution to the power grid,which makes the problem of power quality of the distribution network become more serious.In all power quality problems,voltage sag is the most prominent problem,which has become the main power quality problem affecting the normal operation of the power equipment.However,Low quality voltage level has been unable to meet the needs of industrial production enterprises and precision manufacturing enterprises with highly automated and intelligent electronic devices with computer systems and programmable logic controllers as the core.Although the study of voltage sags is more mature in the traditional grid background,the problem of voltage sags becomes more complicated in the new grid environment.It is necessary to further study the method of voltage sags evaluation and compensation,and to seek the measures of voltage sags in the new grid environment.The structure and operation of the power system are more complicated by the access of the distributed power supply.The factors that cause the voltage sags are no longer easy to see.In order to evaluate the severity of the voltage sags,the voltage factors are required from many aspects,such as amplitude,duration,frequency,phase jump,starting point of the waveform and so on,and it will increase the difficulty of voltage sag assessment.On the other hand,the access of distributed energy storage is also a new opportunity for the control of voltage sags.How to use distributed energy storage to improve the quality of power supply and ensure the stable operation of sensitive loads is an important part of improving the ability of auxiliary service provided by distributed energy storage system.Therefore,in order to evaluate and govern the voltage sags in the new environment,this paper studies the voltage sags evaluation method based on the comprehensive fault rate and the allocation and control method of distributed energy storage participation voltage sags.First,based on the statistical data and simulation results,an evaluation method based on the comprehensive fault rate is proposed,which quantifies the sensitivity of the sensitive load and the effect of voltage sags in the regional power grid,and the evaluation method is verified with a numerical example.Then,the optimal allocation model of location and capacity of distributed energy storage system participating the mitigation of voltage sags is established.The capacity and location of distributed energy storage is optimized with the objective of minimizing the cost,and the balance between the compensation effect of sensitive load and the cost of distributed energy storage system is realized.At last,the method in which distributed energy storage system participating in voltage sags compensation is studied.A joint compensation method of distributed energy storage and DVR is proposed.The advantages of distributed energy storage system and traditional voltage sags compensation are complemented,and the effect and efficiency of voltage sags compensation are improved.The main contents of this paper are as follows:(1)Voltage sag assessment method based on integrated failure rate.For the tolerance of voltage sags and the impact of voltage sags,this paper proposes a voltage sags evaluation method based on the comprehensive failure rate.On the load side,through the simulation of the operating state of the voltage sags generated by the sensitive load in Monte Carlo method,the comprehensive failure rate of the load for the random voltage sags is obtained and used to evaluate the load tolerance.The voltage sags event is simulated by the simulation of the operating state of the sensitive load in the area affected by the voltage sags.In real analysis,the voltage sag event is calculated by weighted average,which will cause the comprehensive failure rate to evaluate the impact of voltage sag events.(2)A distributed energy storage location and capacity allocation method based on particle swarm optimization.On the basis of ensuring the stable operation of the sensitive load in the voltage sags event,the distributed energy storage position and capacity need to be configured to realize the distributed energy storage participation in the voltage sags compensation.In this paper,a location and capacity optimization method for distributed energy storage in voltage sag auxiliary service is proposed.First,the distribution network is modeled and simulated,the optimal compensation node of single sensitive load and the multi sensitive and integrated optimal compensation node are selected,and then the selected nodes are optimized two times by particle swarm optimization.Finally,the distribution location of distributed energy storage is determined according to the optimization results of the position,and the distributed energy storage output is obtained.The optimal result is converted to the capacity allocation ratio of distributed energy storage.The simulation results show that the efficiency and security of the distributed energy storage system for the sensitive load voltage sags are higher than the other contrast group positions generated by the optimized storage energy storage system.(3)Distributed energy storage control method for voltage sag compensation.On the basis of the optimal allocation of distributed energy storage,the control model of distributed energy storage and the joint compensation of distributed energy storage and DVR is established respectively,and the distributed energy storage output of each model is optimized to ensure the compensation efficiency of distributed energy storage in each model.Then the simulation calculation is carried out.According to the voltage information of the sensitive load monitoring points and the comparison of the output information of each compensation device,the results show that the combined compensation of distributed energy storage and DVR is better than the distributed energy storage for compensation in the compensation effect and efficiency,and the compensation ability and the duration of compensation are used.It is superior to traditional compensation only by using DVR. |
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