Research On Steady-state Characteristics Of The Flexible Low Frequency AC Cable Transmission System For Urban Grid

With the emergency of a lot of new load in the urban power grid.It not only puts forward new demands for the power supply capacity of the urban power grid,but also requires the urban power grid to provide power to the central area of the load intensive flexibly and easily.How to improve the transmission capacity based on the original transmission corridor,and satisfy the flexible and controllable power supply,is a problem to be solved in urban power grid.As a new transmission technology,low frequency transmission is expected to become an important method to solve this problem,which is concerned by domestic and overseas scholars gradually.In view of the wide use of underground cable in urban power grid,this paper constructs a flexible low frequency cable transmission system which is applied to urban power grid.Firstly,the structure,basic principle and technical advantages of the flexible low frequency cable transmission system are summarized;Secondly,the steady-state characteristics of low frequency transmission system was analyzed based on the frequency characteristic of power cable ampacity,and then the selection approach of optimal transmission frequency was also proposed.Combined with the specific example it can verify that the selected frequency can not only satisfy the safe and reliable operation of the system,but also graduate the maxium active power in the end of the cable.Finally,the electromagnetic transient equations as well as the control model of the modular multilevel matrix converter based system are simulated in PSCAD/EMTDC.The results demonstrates the effectiveness of the proposed control strategies.The research of this paper relies on the project “Fesibility of the Fractional frequency transmisssion technology in the Global Energy Internet”cooperated with global energy interconnection research institute.A new type of power transmission technology which is suitable for the expansion and transformation of urban power network is explored,which provides a new solution for the expansion of power grid.