针对传统的模块化多电平换流器控制策略过于依赖控制器参数整定,以及传统的模型预测控制中存在权重因子选取困难等问题,提出一种基于模型预测控制的模块化多电平换流器多目标级联式控制策略,对多个控制目标逐级独立优化实现输出电流控制、桥臂环流控制以及子模块均压控制.控制策略在避免权重因子选取的同时还兼顾良好的控制效果.在MATLAB/Simu-link中搭建仿真模型,验证了所提策略的有效性.

提出了一种基于自适应电流预测模型的零序环流抑制策略,该策略适用于共直流母线的并联运行的三电平逆变器.首先构建了零序环流等效模型,分析证明了并联系统的中点电位差和共模电压差为零序环流激励源;随后提出了一种基于预测模型的零共模电压控制方法,兼顾了中点电位平衡的控制效果并改善了并网电流质量,同时对并联系统之间的零序环流进行了有效抑制;其次设计了一种自适应电流预测模型,提高了在参数失配下并网电流的跟踪性能,减少了误差;最后通过MATLAB/Simulink平台搭建仿真模型,验证了所提控制策略的可行性和有效性.

With the high-speed development of digital signal processors, model predictive current control (MPCC) has been widely used in power converters. However, the control robustness of MPCC is poor because of its strong dependence on the model parameters. In this paper, an ultra-local model-free predictive current control (MFPCC) for three-level grid-connected inverters (GCI) with LCL filters is proposed. Based on ultra-local theory, a third-order ultra-local model of the GCI with LCL filters is constructed. Then, a Kalman filter (KF) is introduced to estimate the three perturbations. Moreover, the perturbations are compensated to the predictive current model, thus reducing the number of model parameters involved in the predictive control. Finally, simulation results show that the proposed MFPCC improves the tracking performance of the grid current and strengthens the dynamic response capabilities under the parameter mismatch. Furthermore, the output power quality becomes higher, and the system robustness is also enhanced under noisy environment.

Under the condition of weak grid, the coupling between parallel inverters and grid impedance is easy to cause harmonic resonance, which seriously affects the grid-connected power quality. First, the equivalent circuit model of the multi-inverter parallel system is established, and the mechanism of harmonic resonance is analyzed from the perspective of impedance; through the resonance detection method based on a self-tuning filter, the voltage resonance component of the parallel node is extracted; on that basis, an active impedance is designed to suppress the resonance of the multi-inverter parallel system, which can equivalently construct a virtual impedance branch to improve the grid impedance characteristics at the resonance frequency, and its effectiveness is verified using the impedance stability criterion. Finally, simulation experiments are carried out. The results show that this method can effectively suppress the resonance of the multi-inverter parallel system and can significantly improve the adaptability of inverters to weak grid.