考虑子模块均压约束的混合型模块化多电平换流器功率极限分析

Analysis of maximum power operating region for hybrid MMC considering sub-module balancing constraint

混合型模块化多电平换流器具备降压运行和不闭锁穿越直流故障的能力,子模块均压约束是其降压运行时对稳态功率运行范围起主要限制的运行约束。从满足子模块均压约束的换流器桥臂电流和桥臂电压的特性出发,分析了混合型模块化多电平换流器在降压运行时的功率极限运行范围。提出了快速确定混合型模块化多电平换流器可行功率运行域的计算方法。通过对比解析扫描计算的结果和电磁暂态仿真共同验证了计算方法的准确性和有效性。分析了全桥子模块比例对功率运行极限范围的影响。从功率运行能力的角度提出了全桥子模块最小比例的设计方法。

Hybrid Modular Multilevel Converter(MMC)has the ability to operate under reduced DC voltage and ride through DC faults without blocking IGBTs.Sub-module balancing constraint places the dominant limit on the feasible power transferring region compared to other constraints when it operates under reduced voltage.This paper analyzes the characteristics of the arm current and arm output voltage that meet sub-module balancing constraint,and calculates the corresponding maximum power operating region when hybrid modular multilevel converter operates under reduced voltage.A fast calculation method is proposed to determine the feasible operating region.The effectiveness and accuracy of the proposed method is validated by comparing calculation results with a scanning method and cross-verified by electromagnetic simulation.The impact of the full-bridge sub-module ration on the operating region is analyzed.A new design model regarding full-bridge sub-module minimum ratio is provided from the perspective of power transferring ability.