Topology Analysis And Control Strategy Research For Distribution Network Unbalanced Compensation STATCOM

With the progress of society,modern science and technology,industrial level are getting higher and higher.All the above advances have more and more stringent requirements for power grid quality.At present,the static synchronous compensator STATCOM has been widely used in reactive power compensation,unbalance compensation,harmonic suppression and other power quality management governance fields by virtue of its excellent performance.In this paper,the compensation of three-phase unbalance by STATCOM is studied.In terms of STATCOMs,it also has many different topologies are available,and in the light of different STATCOM topology,Their compensation characteristics,usage scenarios,and control strategies are also different.They need to be compared and analyzed.Therefore,the optimal STATCOM topology can be selected according to the requirements of different application scenarios(the current to be compensated is different;the unbalance degree of the load to be compensated is different;the withstand voltage and current withstand values of the device are different;the DC side voltage is different,etc.)to perform three-phase unbalance compensation.The main working framework of this paper can be briefly described as follows:The first is for the phase-to-phase unbalance problem when the STATCOM compensates for the three-phase unbalance.,a new cascaded STATCOM topology is introduced.In addition to the three-phase cascaded power unit,the new topology also connects a DC side common capacitor in parallel,which can be called slave inverter.,three-phase cascade bridge arm can exchange active power by the slave inverter,and thereby eliminating phase-to-phase unbalance;In this paper,it is considered that the unbalanced compensation range of the topology is mainly limited by the output voltage of the slave inverter,and the related reasons are listed,and the related variables that affect the unbalanced compensation range are analyzed.Because the topology contains the slave inverter,it is necessary to allocate the voltage output relationship between the master inverter and slave inverter reasonably,so the master and slave coordinated control strategy is introduced.Then,problems of unbalance compensation of traditional star-connected/angle-connected STATCOM are studied.Taking star-connected STATCOM as an example,the phasor method is proposed to calculate the zero-sequence voltage to be injected conveniently and quickly by using the geometric relation between output voltage and compensation current,which avoids the computational complexity of traditional method.Because the injection of zero sequence voltage will increase the output voltage of compensation device,which will cause over modulation,this paper takes this as the starting point,establishes the unbalance compensation range standard of the star-connected STATCOM,and discusses the related issues.The DC side voltage control is also divided into three layers.Different from the new topology,the phase-phase balance control of the star-connected STATCOM is mainly accomplished by zero-sequence voltage injection method.Then this paper also discusses the unbalance compensation capability of MMC-STATCOM.In this paper,it is pointed out that the current margin is closely related to the unbalance compensation capacity,and the unbalance compensation range of MMC-STATCOM is discussed.It is pointed out that the DC component of its circulation can be used for phase-phase balance control and the double frequency component can be eliminated.Like the centralized topology described earlier,the current control of MMC-STATCOM also adopts a quasi-PR control strategy,which can track the AC volume quickly and stably.Through the detailed introduction of the above STATCOM topologies,we can analyze and compare them,list their respective advantages and disadvantages,and point out the optimal choice for different three-phase unbalance application scenarios through comparison.Finally,for the several STATCOMs discussed in this article,in addition to building simulink simulation models for simulation verification in the corresponding part,the article also sets out to build the corresponding experimental device,and introduces the corresponding software and hardware design ideas and design results in detail,And finally carried out real-time simulation with the help of RT-LAB.