Research On Steady-state Power Flow Regulation Method Of Power System With Extended SEN Transformer

With the growing penetration of the large-scale renewable and sustainable energy resources and the increasing load of power system,it has been becoming more and more difficult for the dispatch of power generation and the power flow control in the power system,and it may be an effective way to optimize the power flow using power flow controllers.Extended SEN Transformer(EST)is a kind of novel electromagnetic power flow control device,which has more better control accuracy and the larger operational range than traditional ST,and compared with the unified power flow controller(UPFC)based on the technique of voltage source converter,which has advantages of better economy and higher reliability.Therefore,it is of great significance to study the methodology of power flow control with EST for optimizing power flow.Firstly,this paper summarizes the technical principles of electromagnetic power flow control devices such as phase shifters,voltage regulators,and ST,and their various functional characteristics and economy are compared.Secondly,the research status of modeling for ST and its variants are introduced.Finally,the researches of both ST and its variants for power flow control,and the application of UPFC projects in the actual power grid are described.Secondly,the working principle and the tap-changing algorithms of EST are introduced,and then the operational range and control accuracy of both EST and traditional ST are analyzed.Furthermore,from the perspective of simplifying the power flow model of EST,the EST is simplified to be an equivalent circuit of dual voltage source,and thus an EST model suitable for unified iterative power flow solution is proposed which is considering its three main power flow control modes and the operating constraints of EST.The effectiveness of the proposed model is verified in the modified IEEE 6-machine 30-bus system and the control accuracy between traditional ST and EST are compared in the IEEE 54-machine 118-bus system.Subsequently,as for the power system including wind power,the probabilistic models of wind power output and load are established,and the three-point estimation method is used to calculate the probabilistic power flow with EST.And then,in order to improve the predictability of power system and reduce the expected values of active power loss,using the NSGA-II multi-objective algorithm to acquire the better control strategy of EST and its placement under different penetration rates of wind power in the IEEE 7-machine 57-bus system.Finally,considering these cases that short-circuit faults may occur in the power system with EST,so the various short-circuit models of EST are derived using the phase coordinates method.The short-circuit current and the voltage at the receiving end of EST are obtained from the time-domain simulation and the analytic calculation utilizing the proposed model can reach acceptable agreement,confirming its effectiveness.Moreover,the influence of short-circuit currents for power system after single-phaseto-ground and three-phase short-circuit faults are analyzed,and the control strategies for suppressing short-circuit are proposed.