Research And Test Analysis On Control And Protection System Of MTDC Transition Project

With the rapid development of AC-DC hybrid power grid in China, traditional two-terminal HVDC(TTDC) has already not been able to meet the development requirements of power grid. Therefore, it has become the future development direction and urgent need for the AC-DC hybrid power grid to seek more efficient and stable power transmission mode by optimizing the structure of DC transmission system. Compared with TTDC, multi-terminal HVDC(MTDC) transmission system enjoys greater advantages in terms of economy and operational flexibility, but it also brings more problems and requirements to control and protection technology due to its complicated structure and operational mode.At present, a HVDC transmission project under construction in China for the first time has adopted the structure of two poles connected to two AC grids, thus transferring the power to two asynchronous networks through two poles respectively. Due to the power distribution mode of receiving-end, this project can be regarded as transition project of MTDC. This paper, taking the transition project of MTDC as the research object, compares and analyzes its similarities and differences under different power transmission modes of receiving-end in terms of such three aspects as structure and operational mode, control strategy, protection and fault response.This paper firstly analyzes and summarizes the structure features and operational mode of MTDC transition project. In terms of control strategy, it analyzes switch control of AC switching yard under different power transmission modes of receiving-end and conducts steady performance test of mode switch under power transmission, and then deems that the switch process may exert huge risk on the operation of AC-DC system. In terms of reactive power control, by comparing and analyzing the closing and opening test of AC filter under different power transmission modes of receiving-end, it points out that the closing and opening of AC filter under distribution mode of receiving-end is more flexible. In terms of pole control, it analyzes the particularity of DC power control, PPT and current balance control, and verifies the distinctive function of monopole power control through power up-and-down test. Besides, it studies the influence of AC intensity under different power transmission modes of receiving-end and VDCOL control on DC dynamic characteristics, and puts forward advice on parameter conversion of VDCOL control. In terms of protection, it makes a brief overview of protection zone and its configuration, and analyzes the fault response characteristics through DC line fault tests and AC fault tests under different power transmission modes of receiving-end, thus drawing relevant conclusion.