适用于大步长情形下基于模块化多电平拓扑的直流电网高效仿真建模方法

An Efficient Modeling of Modular Multi-level Converter Based DC Grids by Using Larger Time-steps

针对基于模块化多电平换流器构成直流电网的控制保护设计,需要充分考虑系统级和装置级内部的高频电磁暂态过程。传统模块化多电平换流器加速模型由于数值稳定性的限制无法将仿真步长扩大到50μs以上,此外也无法给出系统宽频相量值的波形。为了解决上述问题,该文采用旋转坐标变换提出适用于大步长情形下的基于模块化多电平拓扑的直流电网高效建模方法。该方法可以将仿真步长进一步扩大到100μs以上,继而从建模本质上提高仿真效率,同时又能满足仿真精度的要求。特别地,该方法可以给出交流量瞬时值和高频相量值的波形。该文将该方法用于国内某含有四端柔直系统的大规模交直流的案例测试中,通过仿真验证该建模方法在仿真精度和仿真效率以及灵活性方面的优势。

For the control and protection design of modular multi-level converter(MMC) based DC grids, it is necessary to fully consider the high frequency electro-magnetic dynamics of the system level and the device level. Traditionally, the MMC accelerated model cannot extend the simulation time-step to more than 50 microseconds due to the limitations of numerical stability. Additionally, these models cannot produce the desired wide frequency band phasors simultaneously. To resolve these issues, an efficient model of MMC based DC grids was proposed based on the rotational transform. As a result, this model can extend the time-step to more than 100 microseconds. It can improve the simulation efficiency significantly while satisfy the accuracy expectations. Especially, it can produce instantaneous and wide frequency band phasor waveforms. This method was further applied to a large-scale MMC based AC/DC grid in China integrating four-terminal VSC converters. The simulation results have verified the advantages of this model in simulation accuracy and simulation efficiency.