LCC-MMC混合级联型直流输电系统启动控制策略研究  

Start-up control strategy for an LCC-MMC hybrid cascade HVDC system

作　　者：何平港 牟大林 林圣[1] HE Pinggang;MU Dalin;LIN Sheng(School of Electrical Engineering,Southwest Jiaotong University,Chengdu 611756,China)

机构地区：[1]西南交通大学电气工程学院,四川成都611756

出　　处：《电力系统保护与控制》2022年第22期71-80,共10页Power System Protection and Control

基　　金：国家自然科学基金项目资助(51977183)。

摘　　要：为实现逆变侧采用电网换相换流器(line commutated converter,LCC)和多个并联模块化多电平换流器(modular multilevel converter,MMC)阀组串联的混合级联直流输电系统的安全、可靠启动,提出了一种按照不可控充电和系统控制解锁两阶段划分的启动控制策略。首先建立该类混合结构下直流系统的数学模型。在对低压端MMC不可控充电阶段暂态特性分析的基础上,推导了MMC最大启动冲击电流和预充电时间的等效计算公式,并根据最大冲击电流和预充电时间为MMC启动过程中限流电阻的选取提供依据。其次,在系统级控制器解锁至系统稳态运行阶段,针对MMC并联组在控制器解锁时产生的不平衡启动电流问题进行了分析,提出一种基于不同换流器间控制时序配合与自适应MMC功率参考值的启动优化策略。最后,通过PSCAD/EMTDC仿真结果表明,所提启动方案可以有效实现混合级联型直流输电系统的平稳启动。To realize safe and reliable start-up of a hybrid cascaded DC transmission system in series with line commutated converter(LCC)and parallel modular multilevel converter(MMC)valves on the inverter side,a start-up control strategy based on the two stages division of uncontrollable charging and control unlocking is proposed.First,the mathematical model of the hybrid DC transmission system is established.Based on the analysis of the transient characteristics of the uncontrollable charging stage of the MMC at the low-voltage end,the equivalent calculation formulas of the MMC maximum start-up impulse current and pre-charge time are deduced.Then the selection basis of current limit resistance in the MMC start-up process is provided according to the maximum impulse current and pre-charge time.Second,from the unlocking of the system controller to the steady-state operation stage,the unbalanced start-up current problems between MMC parallel groups when the controller is unlocked are analyzed.Then an optimized cooperation strategy based on the control sequence coordination of different converters and adaptive MMC power reference valve is proposed.Finally,PSCAD/EMTDC simulation results show that the proposed start-up scheme can effectively realize the smooth start-up of a hybrid cascaded DC system.

关 键 词：混合级联型直流输电系统 限流电阻 不平衡电流 启动优化策略 

分 类 号：TM721.1[电气工程—电力系统及自动化]