| The promotion of electric power alternative,represented by electric heating technology,is important for national defense against air pollution,improving environmental quality and adjusting energy structure.However,all kinds of electric heating equipment with random intermittent and high-power characteristics,such as electric water heaters,fixed frequency air source heat pumps and variable frequency air source heat pumps,large-scale and disorderly access to the grid,will have a serious impact on the power quality of regional distribution network and hinder the promotion of electric heating projects.This thesis analyses the power quality problems arised from large-scale application of electric heating,and puts forward corresponding countermeasures for each problem.The main contents are as follows:(1)According to the electrical characteristics,electric heating equipment is divided into resistance type,constant frequency compressor type and variable frequency compressor type.The main research objects of this thesis are fixed frequency and variable frequency air source heat pumps.The power quality emission characteristics of air source heat pumps are analyzed from topological analysis,simulation modeling and measurement results,and the interaction between power quality and power quality of the power grid is simulated.(2)Aiming at the inrush current impact of the fixed frequency air source heat pumps arise from large-scale application,a soft start method of fixed-frequency compressor based on chopping control technology is studied.In order to solve harmonic problem arised from large-scale application of variable frequency air source heat pumps,the control strategies of installing mono-tuning harmonic filters and installing active power filter are analyzed.(3)In view of the reactive power and active power problems arised from largescale application of electric heating loads,various power quality reactive power compensation devices and their advantages and disadvantages are introduced.A demand response control strategy for electric heating loads is proposed,in which different types of electric heating loads have different control methods.And the control effects are analyzed.(4)Aiming at the three-phase unbalance problem arised from large-scale application of electric heating loads,a three-phase allocation strategy is proposed for three-phase unbalance caused by electric heating users based on hierarchical clustering method and traversal algorithm,which can alleviate the three-phase unbalance problem in the early planning stage.And a low-voltage station user automatic commutation strategy considering the phase index is proposed to deal with the three-phase unbalance in the low-voltage station area in real time.The analysis in this thesis can be applied in the actual coal-to-electricity project,effectively solve the harmonic,voltage,frequency and three-phase unbalance problems caused by large-scale application of electric heating loads,which has high engineering application value,and is of great significance to increase the coverage of electric heating loads,promote electric power alternative projects,and ultimately improve the level of electrification in China. |
