Multi-terminal DC Transmission System Harmonic Analysis And Software Development

With the capacity and transmission distance of the power grid increasing,HVDC technology has been more and more widely used.MTDC is an important direction for the development of HVDC technology.LCC-HVDC has the advantages of high voltage level,large transmission capacity and long transmission distance.At this stage,LCC is widely used in the MTDC transmission project,and the multi-terminal HVDC transmission operating characteristics still need further study.Harmonic current is an important indicator of power grid operation.Harmonics in HVDC project cause additional losses,affecting equipment life,interference,communications hazards and so on.In this paper,the calculation method of steady-state harmonic current of DC network in LCC-MTDC transmission system has been studied and the corresponding calculation software has been compiled.Firstly,this paper introduces the calculation method of the steady-state parameters of the main loop in the MTDC transmission system,which is the basis to analysis the steady-state of the HVDC transmission system.Then the mathematical model of the main equipments in DC network of HVDC system is introduced.The calculation method of line steady-state parameters of frequency dependent phase model based on overhead lines is introduced in detail.The design method of passive filters in DC engineering is introduced.Then,based on the switch function method,the AC-DC harmonic coupling mechanism of HVDC transmission project is studied in detail.The accuracy of the mainstream AC-DC decoupling algorithm is analyzed.After that,the method to calculate the harmonic current in the DC network of a MTDC system based on the 3-pulse model is introduced.The error of calculating the harmonic of the DC network in a MTDC system based on the 3-pulse model is still large,but it can correctly reflect the distribution rule of harmonic current in DC network of MTDC system.This method can be applied to the initial design phase of MTDC transmission project.Finally,the the DC network harmonic current calculation software of MTDC transmission system is compiled,and introduces the software design and development process and instructions.