适用于少子模块混合型MMC直流故障穿越的均压调制策略

Voltage equalization modulation strategy for DC fault ride-through of hybrid MMC with minority submodules

针对混合型模块化多电平换流器(HMMC)在中低压场景子模块个数受限以及直流故障穿越期间的电容电压平衡问题,提出适用于少子模块HMMC直流故障穿越的调制技术以及直流故障穿越期间的电容电压平衡控制方法。从虚拟半桥子模块角度对全桥子模块拓扑进行解耦,统一HMMC的内部拓扑。基于虚拟调制改进载波移相脉宽调制方法,提出适用于HMMC多工况运行模式切换的混合调制技术。进一步考虑直流故障穿越期间的子模块电容电压平衡需求,基于优化子模块充、放电能量分布的思想,重构脉冲映射关系,提出分层脉冲自适应平衡控制方法。仿真结果表明,所提策略实现了少子模块HMMC直流故障穿越,并有效保障了直流故障穿越过程中子模块的动态电容电压平衡。

Aiming at the limited number of submodules of the hybrid modular multilevel converter(HMMC)in medium-and low-voltage scenarios and the problem of capacitor-voltage balance during DC fault ridethrough,a modulation technique suitable for HMMC with minority submodules and a capacitor voltage balance control method during DC fault ride-through are proposed.The full-bridge submodule topology is decoupled from the perspective of virtual half-bridge submodule to unify the internal topology of HMMC.Based on the improved carrier phase-shifting pulse width modulation method of virtual modulation,a hybrid modulation technology suitable for HMMC multi-operating mode switching is proposed.Furthermore,considering the capacitor voltage balance demand of submodules during DC fault ride-through period,the pulse mapping relationship is reconstructed based on the idea of optimizing the submodule charge and discharge energy distribution,and a hierarchical pulse adaptive balance control method is proposed.The simulative results show that the proposed strategy realizes the DC fault ride-through of HMMC with minority submodules,and effectively guarantees the dynamic capacitor voltage balance of the submodules during the DC fault ridethrough process.