Digital-Analog Hybrid Simulation Of DC Transmission System

With the rapid development of ultra-high voltage direct current transmission in China,large-scale connection of new energy to the grid,emergence of various new power electronic devices.The characteristics of DC transmission system have changed deeply.The new characteristics,such as the interaction between the receiving and sending ends of DC,the coupling between AC-DC and between multi-loop DC,are gradually appearing and becoming more and more complex,which puts forward higher requirements for the time domain simulation of the dynamic characteristics of DC transmission engineering.People accurately understand and grasp the mechanism and characteristics of DC transmission system depends on the improvement of simulation technology.Due to the limitations of single digital simulation or physical simulation,the digital-analog hybrid simulation,which can combine the advantages of digital simulation and physical simulation has become a powerful tool for studying DC transmission system.In the digital-analog hybrid simulation of DC transmission system,interface system is used to connect the digital subsystem and the physical subsystem.The stability and accuracy of the interface system under various working conditions are the key problems.In this paper,the DC power interface is designed for the digital-analog hybrid simulation of DC transmission system,and simulation research is carried out on three different types of high voltage direct current(HVDC)transmission system based on line commutated converter(LCC),modular multilevel converter(MMC),and LCC-MMC hybrid.(1)The principle of digital-analog hybrid simulation and interface algorithm is analyzed.A DC power interface based on H bridge is designed.The output performance,stability and accuracy of the designed DC power interface are verified by simulation.(2)The working principle,mathematical model and control strategy of LCC are studied.The digital-analog hybrid simulation system of LCC-HVDC is built,and the simulation results of the system under various working conditions are compared with the pure digital simulation of the original system,which verifies the effectiveness of the digital-analog hybrid simulation of LCC-HVDC system.(3)The working principle,mathematical model,double-loop control strategy and modulation mode of MMC are studied.MMC-HVDC and LCC-MMC-HVDC digital-analog hybrid simulation systems are built respectively,and their effectiveness is verified by comparing with pure digital simulation of the original systems.Aiming at the digital-analog hybrid simulation of LCC-MMC-HVDC system,an interface simulation method suitable for LCC start-up,locking and phase shifting process is proposed.The validity of the proposed method is verified by simulation.