光伏发电MPPT失效现象分析

Analysis of Failure of Maximum Power Point Tracking in Photovoltaic Power Generation

为充分发挥光伏电池的效能,光伏发电系统需采用最大功率点跟踪控制,其中扰动观察法因其简单有效而得到广泛应用。针对扰动观察法搜索方向出错而导致算法失效的现象进行了理论和仿真研究。基于光伏电池小信号模型、解耦环境因素变化和人为扰动电压产生的输出功率增量,通过分析2种功率增量对扰动观察法搜索方向的作用,获得搜索方向出错的机理。进一步分析了光照强度变化的速率、持续时长对算法搜索方向错误次数、错误概率以及光伏发电系统能量损失的影响。研究结果表明,环境因素变化导致的光伏电池输出功率增量与人为扰动电压带来的功率增量相反,且前者占主导地位,是算法搜索方向出错的根本原因。经统计,这种失效现象导致的最大能量损失可达6.47%,搜索方向最大错误概率可达100%。此研究对于进一步改进扰动观察法具有良好的指导意义。

It is necessary to employ the maximum power point tracking （MPPT） method to capture the maximum power from solar arrays.The Perturb and observe （P＆O） method is one of the MPPT methods widely used because of its simple and effective performance. In this paper, the failure due to incorrect searching directions of P＆O method is studied through theoretical analysis and simulation. Based on the small signal model of PV ceils, the output power increments caused by the environmental factors change of decoupling and designed voltage distur-bances, the forming mechanism of the incorrect searching direction is obtained by analyzing the effect of the above two power increments on the calculation of searching direction. Furthermore, the influence of the change speed and duration of the solar irradiance on the number of searching errors, the error probability and the energy loss of the PV power system are analyzed. The resuits show that the searching direction will be incorrect if the increment of output power of PV cells caused by solar irradiance changing is opposite to and larger than the one caused by designed voltage disturbance. It is found that the maximum energy loss is 6.47% and the maximum error probability is 100%. The study is of guiding significance to further improvement of the P＆O method.