带储能的混合级联型光伏逆变器的控制方法研究

Distributed photovoltaic (PV) systems will be an important form of energy supply in the future. But the difference in the characteristic and decay of each single PV cell, uneven illumination and the fluctuation in the intensity of the illumination all have impact on the PV system’s efficiency and stability. Conventional approach of suppressing the power fluctuation in PV system is to connect the PV cells and super-capacitors in parallel in dc side through DC/DC converters, and then connect to the grid through a single DC/AC converter or supply power to the load independently. This project proposes a hybrid multilevel PV inverter using cascaded H-bridges to connect PV cells and super-capacitors. The nature of this topology is connecting these two parts in ac side in series. . Connecting low-voltage PV cells with cascaded H-bridges in order to obtain relatively higher output voltage, can bring higher efficiency of each single PV cell, less harmonics, smaller output filter and transformer, and apply power devices of lower voltage. Adding super-capacitors into the cascaded PV inverter can further increase the output levels besides suppressing power fluctuation. This project plans to study the characteristic of this topology, its control method and the optimized capacity configuration, intending to provide an inverter with higher efficiency for distributed PV systems with energy storage. This work can develop the theory and practice of PV generation system, and can lay foundation for the industrial production of cascaded PV generation systems with energy storage.

分布式光伏发电是未来能源供给的重要形式，但是光伏电池特性及衰减的不一致、光照不均匀、光强波动等都影响了传统光伏发电系统的效率和稳定性。平抑功率波动的常规做法是将光伏电池和超级电容在直流侧并联，然后经单一的逆变器并网或者向负载供电。本项目提出一种利用H桥级联多电平拓扑结构，将光伏电池与超级电容混合级联的光伏逆变器，其实质是两者在交流侧的串联。将低压的光伏电池通过H桥级联的方式输出较高的电压，能够提高单个光伏电池的发电效率、降低输出谐波、减小输出滤波器和变压器的体积，还可以使用低成本的低压功率器件；级联电路中加入超级电容既能平抑功率波动，又进一步增加了输出电平数。本项目研究这种混合级联逆变器的拓扑结构特点、控制方法和容量比例优化配置，以期为带储能的分布式光伏发电提供一种更高效的逆变器结构。研究成果丰富了光伏发电系统的理论和实践方法，为带储能的级联型光伏发电系统的工业化奠定基础。

为提高光伏发电效率、减小发电系统体积、降低成本，本项目提出一种新的混合级联型的逆变器结构，将光伏电池和超级电容采用H桥级联的方式构成光伏发电系统，并研究这种光伏逆变器的控制方法。. 首先，根据不同类质单元间的工作特点，应用相量法，设计了混合级联光伏逆变器的工作原理，给出了系统稳定边界条件，从而研究级联的光伏电池与超级电容之间的能量控制策略。. 其次，基于电导增量法，研究了在级联的光伏单元之间实施分散的最大功率跟踪控制的方法，得到了单个光伏单元的控制信号修正方法。. 然后，根据混合级联光伏逆变器的工作原理，设计了一种协同调制方法，利用特定谐波消去调制的精确性和PS-PWM调制的高等效开关频率特性，将二者结合，利用光伏单元的输出补偿储能单元输出中未被消除的低次谐波，降低逆变器的总输出谐波。. 最后，通过仿真和实验，对混合级联光伏逆变器的控制方法进行验证。研究成果丰富了级联多电平拓扑结构的应用理论与实践方法，且能应用于分布式和集中式光伏发电系统。.