Research On Electromagnetic Transient Analysis And Control Method Based On Sen Transformer Of EOLT

Climate challenges and fossil fuel consumption have been driving the large-scale integration of solar power,wind power,and other renewable energy sources in the power system.However,the intermittency,variability,and uncertainty of these new energy sources cause the voltage regulation and the power flow control(PFC)in modern power systems to be more and more difficult.The unified power flow controller(UPFC)is the most versatile power flow controller.However,the relatively high costs involving installation and operation for UPFC might limit its widespread application.The electronic on-load tap-changer based Sen Transformer(EST)is lower in cost and has almost the same functionality as UPFC.Meanwhile,The EST may increase the number of the operational position about compensation voltage since the windings can achieve bidirectional connection through the electronic on-load tap-changer(EOLTC),which makes PFC more flexible and accurate.The response speed of the PFC may be improved by EOLTC.Therefore,it is undeniable that the EST might be an attractive power flow controller.Firstly,this paper summarizes and analyzes the research background,significance,and current situation of Sen Transformers(ST)and its variants,highlighting the advantages and features of the electronic on-load tap-changer based Sen Transformer(EST).By illustrating the current situation for modeling of ST and its variants,the necessity of transient modeling for EST is clarified.By examining the application of EOLTC in transformer,phase-shifting transformer,and ST,the significance of analyzing switching logic for EOLTC in EST is demonstrated.By discussing the current research situation of ST control methods,the importance of studying EST control methods is shown.Secondly,the working principle of EST is introduced,and its topology,operation principle,the region of PFC,and the regulation modes of PFC are analyzed.Furthermore,based on the thyristor switch model and unified magnetic circuit principle proposed in this paper,an electromagnetic transient model for EST is established.This model takes into account the reverse recovery process of thyristors and the multiwinding coupling effect.Analytical calculations and time-domain simulations are performed using MATLAB,ANSYS/Simplorer,and PSCAD/EMTDC,verifying the effectiveness of the proposed model.Thirdly,the switching logic of EST is analyzed,including the basic switching logic,the impact of overlap angle and short circuit on the tap-changer,ultimately providing an optimal switching angle selection method for EST.Analytical calculation and timedomain simulation are conducted using MATLAB and PSCAD/EMTDC,validating the effectiveness of the proposed switching logic and optimal switching angle selection method.Additionally,the effects of multi-winding coupling and thyristor reverse recovery on the switching process are analyzed,and the characteristics of overlap angle and short circuit on the tap-changer under different power factors are discussed.Finally,based on the three regulation modes of EST during operation and the proposed optimal switching angle selection method,control methods for different EST regulation modes are designed.Using MATLAB/Simulink,the effectiveness of the proposed control methods is verified in a power system containing EST.Furthermore,a comparison and discussion of the active and reactive control regions of EST with traditional ST are conducted,and the differences and advantages of EST compared to ST are analyzed.