单相级联 H 桥多电平光伏并网逆变器控制方法磁

摘要

The cascaded H‐bridge multilevel converter has attracted much attention in grid‐connected photovoltaic appli‐cations .The main reason is that each H‐bridge needs isolated DC‐sources ,which can be easily given by PV modules .The converter structure has high efficiency ,low current harmonic ,and is very flexible and modular .Since the PV strings operate at different maximum power points ,there is an inherent power imbalance that can produce voltage drift of the DC‐links .Mo‐reover that all the cells have the same circulating current ,hence it is not possible to implement an independent grid current control loop to control each DC‐link voltage .In this paper a control method for single‐phase cascaded H‐bridge multilevel converter for grid connection of photovoltaic systems is analyzed .Each DC‐link voltage is compared to the corresponding voltage reference ,and the sun of the errors is controlled through a PI controller that determines the grid current provided by the multilevel converter .The proposed control idea to overcome the drift problem in DC‐link voltage ,is to compensate in the modulation stage by changing the modulation index .Simulation results are presented to support the control method .%级联 H 桥多电平逆变器的效率高、电流谐波小，易于扩展和模块化。各 H 桥直流侧的独立电源便于由论伏组件提供，这些优点使其在光伏并网发电系统中的应用引起重视。由于各级 PV 组件在不同的最大功率点运行，造成功率不平衡从而产生直流侧电压波动。另外，由于各个功率单元相串联，输出同一个并网电流，因此不可能由电流环直接去控制各个功率单元的直流侧电压。本文分析了单相级联 H 桥多电平光伏并网逆变器控制方法，将各单元直流侧电压与参考电压偏差之和经调节后转换为输出电流参考值，再采用可变调制系数抑制直流环节电压漂移。仿真结果证明了这种扩展方法是有效的。