CAJ | 학술논문

该文介绍基于模块化多电平换流器(modular multilevel converter,MMC)的直流电网启动预充电过程.直流电网启动时,若有源站和无源站解锁顺序或控制策略不当,都将产生较大的冲击电流和电压跌落;同时若无源站解锁后采用常规控制策略,将导致无源站站间直流电压和子模块电容电压出现振荡.分析解锁后充电过程中有源站和无源站之间的能量转移和交换规律以及无源站间电压振荡机理.提出直流电网有序解锁方案和改进多电平调制算法,同时设计无源站闭环能量平衡控制策略.在PSCAD/EMTDC中建立一个基于MMC的4端直流电网模型,在该模型中对所提启动控制策略进行仿真验证.结果表明,所提出的闭环控制能够保证解锁过程中无源站站间电压振荡得到有效抑制,确保系统直流电压和所有换流站子模块电容电压都能按照设定值进行充电,实现直流电网平稳快速启动.
해문개소기우모괴화다전평환류기(modular multilevel converter,MMC)적직류전망계동예충전과정.직류전망계동시,약유원참화무원참해쇄순서혹공제책략불당,도장산생교대적충격전류화전압질락;동시약무원참해쇄후채용상규공제책략,장도치무원참참간직류전압화자모괴전용전압출현진탕.분석해쇄후충전과정중유원참화무원참지간적능량전이화교환규률이급무원참간전압진탕궤리.제출직류전망유서해쇄방안화개진다전평조제산법,동시설계무원참폐배능량평형공제책략.재PSCAD/EMTDC중건립일개기우MMC적4단직류전망모형,재해모형중대소제계동공제책략진행방진험증.결과표명,소제출적폐배공제능구보증해쇄과정중무원참참간전압진탕득도유효억제,학보계통직류전압화소유환류참자모괴전용전압도능안조설정치진행충전,실현직류전망평은쾌속계동.
This paper studied the startup process of DC grid based on modular multilevel converter (MMC). If the DC grid is deblocked in two-terminal system logic, the pre-charging process will produce a higher inrush current causing a severe voltage dip in both AC and DC system potentially exceeding the allowing limits. Also if the passive terminal uses the traditional control strategy after unlocking the station, there are voltage oscillation among the passive terminals. The energy transferring and exchanging among active and passive stations during the charging process and the mechanism of the voltage oscillation among passive terminals are analyzed. A close-loop precharge control strategy was proposed to eliminate voltage oscillations in the DC voltage of the system and the voltage of the SMs. A four-terminal DC grid model was established on PSCAD/EMTDC. Then the control strategy was verified by the simulation in the proposed model. The simulation results proves that the proposed control strategy have good dynamic performance and can effectively suppress the voltage oscillation.