Research On Key Problems In Solid State Transfer Switch

With the increase of sensitive loads and high-tech equipment,users requirements for power quality are getting higher and higher.At the same time,a large number of non-linear and impact-type loads have adversely affected the power quality of power systems,and power quality problems have become one of the problems that need to be solved.Customized power technology,as a stable and reliable power supply technology for specific users,has attracted widespread attention from scholars at home and abroad.Solid state transfer switch are one of the important components of customized power technology equipment.The solid state transfer switch is composed of a thyristor valve and a vacuum circuit-breaker in parallel.The normal operation of the thyristor valve is one of the key technologies for ensuring the normal operation of the solid state transfer switch.This paper mainly studies the grading and synchronous triggering of series thyristors.Based on the study of thyristor dynamic switching characteristics,static blocking characteristics and corresponding thyristor charge control model,the reasons for the voltage unbalance of the series thyristor valve during the operation of the solid state transfer switch are analyzed and a grading scheme is proposed.And the grading scheme is that using parallel R branch for static grading and parallel RC snubbers branch for dynamic grading.The RC model is constructed and the rationality of the proposed grading scheme is illustrated by theoretical analysis and formula derivation.Finally,two models of series thyristor grading are built by Saber simulation software.it is demonstrated by comparing the voltage waveforms around the thyristors before and after grading that the grading scheme is effective ande accurate?By comparing the advantages and disadvantages of the three trigger modes and according to the actual application of the solid state transfer switch(SSTS),the photoelectric trigger manner is used to trigger the thyristors.The five-pulse coding mode used for photoelectric triggering can reflect the state information of the thyristor more than the three-pulse code.It is mainly composed of Valve Base Electronics,Photoelectric Signal Conversion,Light Singnals Transmission and Thyristor Electronics.Thyristor Electronics is located on the high voltage side of the thyristor,which mainly performs thyristor triggering,voltage detection,BOD protection,and voltage change rate(du/dt)detection function.The accuracy of each detection circuit and trigger circuit is verified by Saber and Quartus II simulation software.Valve Base Electronics is located on the low voltage side and includes a dual pulse generator,a single pulse generator,a timing indicator,and a du/dt protection logic.The Quartus II simulation software verifies that the triggering system of the valve-based electronic device(VBE)can complete the generation of single-pulse,double-pulse and return signals,indicating the accuracy of the triggering scheme.Based on the above theoretical analysis,three thyristor series grading experimental platforms were built.The data waveforms before and after static and dynamic grading are compared and analyzed using a trigger signal with a dispersion of less than 50 ns.The experimental data show that the grading scheme proposed in this paper can effectively solve the problem of voltage unbalance of the series thyristor,effectively suppress the generation of overvoltage,and has good performance of simple,effective,practical and economical application.The theoretical analysis of the series thyristor grading and photoelectric triggering scheme can be applied to various places where the series thyristor is used,and the application prospect is considerable.