基于比例降阶准谐振的MMC环流抑制策略

模块化多电平换流器三相桥臂之间存在的数值较大的二次谐波电流即环流,不仅会影响换流器的稳定运行,同时增加了系统损耗。为抑制该环流,本文提出了一种基于比例降阶准谐振的MMC环流抑制器。首先借助二阶广义积分器检测并提取环流中的负序二倍频分量,再利用克拉克变换将三相环流变换到两相静止坐标,再利用降阶准谐振控制器实现对环流的无静差跟踪,得到参考电压修正量。该控制器能够快速精确地从环流分离出负序二倍频分量,且数字化实现简单。最后,在PSCAD/EMTDC搭建11电平MMC-HVDC仿真模型,验证了比例降阶准谐振控制器的有效性。

MMC Circulating Current Suppression Strategy Based on Proportional Reduced Order Quasi-resonant

There is large value of second-order harmonic current that flows through the three phase arm of modular multilevel converter, namely circulating current, which not only influences the stability of the converter, but also increases the losses of HVDC system. In order to suppress the circulating current, a proportional reduced order resonant controller is proposed in this paper. Firstly, the negative double line frequency in circulating current is detected and extracted by the second-order generalized integrator, after which the three-phase circulating current is transformed to DC component by reference frame transform of three-phase to two-phase coordinates. Subsequently, the proportional reduced order resonant controller is applied to achieve precise tracking of circulating current, and the correction of reference voltage is obtained. This controller can accurately and rapidly extract the negative sequence two octave component and is simple to implement.