计及零直流电压控制的混合型MMC-HVDC输电系统短路电流计算方法

Short-circuit Current Calculation Method for FHMMC-HVDC Transmission Systems With Zero DC Voltage Control

混合型模块化多电平换流器通过零压控制限制直流侧故障电流,为准确分析计算故障后直流侧电流,考虑不同阶段控制系统作用建立其等值模型,并设计故障电流求解计算方法。在零压控制前,构建混合型MMC的串联RLC等值模型,利用受控电流源表征交流馈入能量对故障电流的影响;在零压控制后,分析上下桥臂电压动态调整对故障电流的影响,构建相应混合型MMC等值模型提高计算精度。采用状态空间方程计算2个阶段的直流短路电流,通过电容电压置零来计及零压控制后子模块投切引起直流侧电压复零的特性。基于MATLAB/Simulink仿真平台搭建了双极混合型MMC直流输电系统,在不同工况下通过与详细电磁暂态仿真结果对比,验证了所提短路电流计算方法的准确性。

The half and full bridge hybrid modular multilevel converter(FHMMC)limits the DC-side fault current through the zero-voltage control.To accurately analyse and calculate the post-fault DC-side current,an equivalence model of the control system is established considering the roles of the control system in different stages and a fault current solution calculation is designed.Before the zero-voltage control,a series RLC equivalent model of the FHMMC is constructed to characterise the effect of the AC feed energy on the fault current using a controlled current source;After the zero-voltage control,the effect of the dynamic adjustments of the upper and lower bridge arm voltages on the fault current is analysed and the corresponding FHMMC equivalent model is constructed to improve the calculation accuracy.The state space equations are used to calculate the DC short-circuit currents in the above two stages,and by setting the capacitor voltage to zero the characteristic is accounted for of the DC side voltage back to zero caused by sub-module throwing after the zero-voltage control.A bipolar FHMMC-HVDC transmission system is built based on the MATLAB/Simulink simulation platform.The accuracy of the proposed short-circuit current calculation method is verified by comparing the results with the detailed electromagnetic transient simulation results under different operating conditions.