Research And Design Of STATCOM Control Method For Three Phase Four Wire System

With the rapid development of social economy,all kinds of power electronic devices such as nonlinear devices are widely used in three phase four wire system in distribution network,these devices not only consumes reactive power,but also produces a large amount of harmonic component.The existence of all kinds of single-phase load,the three-phase unbalanced load or the system lacks,produces zero sequence current,make the distribution network neutral current is too large,seriously affect the power quality.Static synchronous compensator(STATCOM)as a new generation of power electronic compensation device,its application in three phase four wire system gradually become a hot research topic.The working principle of STATCOM are analyzed in this paper,selected the topological structure of split capacitive three bridge arms as main circuit topology of STATCOM.It used direct current control method,designed with capacitive voltage regulation of triangle wave tracking modulation method,not only effectively reduce the switching loss,make the output current harmonic contain quantity is little,and can adjust the dc side capacitor voltage in real time.In three phase four wire system,based on the instantaneous reactive power theory of IP-IQ operation method and the improvement,to zero sequence component separated then,used in three phase four wire system,the simulation and experiment show that this method can rapidly and accurately detect the reactive power and harmonic current.Two PI control are designed in this paper,the upper and lower capacitance uniform control and dc side voltage balance control always adopts the moving average filtering of PI control method,effectively solve the problem of the dc side capacitor voltage balance.Through PLECS simulation and experimental research,the results are verified by design of three phase four wire system STATCOM device not only can real-time reactive power compensation and harmonic current,eliminate system line current,and fast response,high compensation precision.At the same time proved that the designed dc side capacitor voltage balance control method is feasible and effective.