针对模块化多电平换流器(modular multilevel converter,MMC)在电平数很高时电磁暂态离线仿真效率低下的问题,提出一种基于戴维南等效的MMC电磁暂态整体建模方法。具体而言,在建立MMC戴维南等效模型的过程中:1)假设MMC中全部开关器件都具备理想的关断特性(也即关断电阻无穷大);2)采用同样绝对稳定的后退欧拉法来替代通常采用的梯形积分法对子模块电容进行离散化;3)结合1)和2),提出一种计算复杂度与MMC桥臂子模块数相同的高效排序均压算法;4)针对所提出模型的特点,提出一种精确的MMC闭锁仿真方法。所提MMC整体模型的计算复杂度随着电平数的增加线性增长。在PSCAD/EMTDC下与MMC详细模型仿真对比表明,所提MMC整体模型的暂稳态最大精度误差在2‰以内,并且在仿真121电平MMC时所提模型的加速比在2 770倍以上。
In order to further speed up the electromagnetic transient(EMT) model of the modular multilevel converters(MMC) over the previously developed Thévenin's equivalent algorithms. The integral MMC model was proposed addressing the following four features: 1) assuming the switches of MMC to be ideal if they are switched off; 2) using the A-stable Backward Euler Method(BEM) to discretize the sub-module capacitors instead of the Trapezoidal Rule(TR); 3) an efficient ranking based MMC capacitor voltage balancing algorithm was proposed based on 1) and 2) to work with the MMC model; 4) using the diodes with interpolation functions to simulate the MMC blocking mode. Simulations on PSCAD/EMTDC validate its accuracy and speedup factor by testing over the fully detailed MMC model, the maximum steady and transient states errors are less than 2‰, and the proposed model is 2 770 times faster over the 121-level fully detailed model.