单级式光伏并网逆变系统中的最大功率点跟踪算法稳定性研究

单级式光伏并网逆变系统具有拓扑简单，成本较低的优点。但是这种系统中只存在一个能量变换环节，太阳能最大功率点跟踪(Maximum power point tracking, MPPT)、电网电压同步和输出电流正弦度等控制目标要求同时得到考虑，实现较为复杂。该文提出了一种改进的MPPT算法，在实现上述功能的同时，显著提高了单级式光伏并网逆变系统在光照强度快速变化时的稳定性。该算法的改进主要在于稳态情况下，调整光伏阵列工作点时根据增减方向分别选取合适的步长值；动态情况下，采用前馈方法检测光照强度突变过程，从而迅速改变并网系统运行状态以避免母线电压崩溃现象。基于PSIM仿真平台，对比了定步长MPPT算法和新算法，在阐述算法改进的基础上给出了仿真结果。实验室还建立了300Wp的单级式光伏并网逆变系统，应用全数字化DSP控制技术和改进MPPT算法，实现了系统的并网和可靠运行。仿真和实验结果表明，应用改进MPPT算法的单级式光伏并网逆变系统能够准确跟踪太阳能电池最大功率点，并具有较好的稳定性。

Research on the Stability of MPPT Strategy Applied in Single-stage Grid-connected Photovoltaic System

Single-state grid-connected photovoltaic (PV) system has advantages such as simple topology, low cost, etc. However, this kind of system has only one stage of power conversion and all the control objectives need to be considered simultaneously, such as maximum power point tracking (MPPT), synchronization with the utility voltage and harmonics reduction for output current. Then the complexity of control strategy is increased. This paper proposes a modified MPPT strategy, which remarkably improves the stability of the single-state grid-connected PV system during rapidly changing process of light intensity, with realizing all the control objectives. In steady state, the modified strategy tracks the recent maximum power point of the PV panel by adjusting the output power of the inverter, in which step length changes according to the tracking direction; in dynamic state, by detecting step change of insolation with feed-forward method, the modified strategy is able to rapidly reset the reference value of inverter output power to avoid DC-link voltage collapse phenomenon. Comparing the novel strategy with constant-step MPPT strategy, this paper illustrates the improvement of the new strategy based on PSIM simulation platform. Experimental results also show the high stability and high efficiency of this modified strategy applied in single-stage grid-connected PV system.