一种改进CDSM拓扑开关损耗不均的调制策略

Improved Modulation Strategy for CDSM Topology Switching Loss Unevenness

为了实现柔性直流系统直流侧双极短路故障清除,目前已有不少具有故障阻断能力的子模块,如钳位型双子模块CDSM(clamped double sub-module)等的拓扑被提出。由于新型子模块结构区别于半桥型子模块HBSM(half-bridge sub-module),导致其调制策略并不能完全适用。在传统最近电平调制NLM(nearest level modulation)策略的基础上,提出了适用于CDSM的NLM策略。针对CDSM拓扑存在2种输出UC电平的情况,设计了一种改进的NLM调制策略,可以有效地避免器件导通概率不同导致的功率损耗不均问题。最后,以CDSM拓扑为例,在PSCAD/EMTDC软件中搭建CDSM-MMC仿真模型,验证了所提调制策略的正确性。

In order to realize the bi-polar short-circuit fault clearing of a flexible DC system,many sub-module topologies with a fault blocking capability have been proposed at present,such as the clamped double sub-module(CDSM).Since this novel sub-module structure is different from the half-bridge sub-module(HBSM),its modulation strategy is not fully applicable.Based on the traditional nearest level modulation(NLM)strategy,an NLM strategy for CDSM is proposed.Considering that there are two kinds of output UClevel settings for the CDSM topology,an improved NLM strategy is designed,which can effectively avoid the power loss unevenness caused by different device conduction probabilities.Finally,the CDSM topology is taken as an example,and a simulation model of CDSM-MMC is built using software PSCAD/EMTDC,which verifies the proposed modulation strategy.