Single-stage Photovoltaic (pv) Grid Type Micro Inverter

Distributed photovoltaic (PV) grid-connected inverter technology is a rapidly developed hot topic in recent years, which integrates micro-inverters (Power level is in200-400watt) and single PV module to realize the modularization and the applications for home uses more easily. Distributed PV grid-connected enjoys increasing attention for its dominant characteristics including high efficiency, high stability, high flexibility of expansion, high simplification in assembly, which enables the integration of PV roof and PV architecture to achieve a great potential in small-medium power level applications.Under this background, this paper mainly studies the micro-inverters, which are the core modules of distributed PV grid-connected power generation system. Focusing on the issues about micro-inverter efficiency, safety and stability, high quality, researches on the topics of system structure of micro-inverters, quasi-proportion-resonance (Q-PR), and maximum power point tracking (MPPT)are implemented, which take the characteristics of micro-inverters like low input voltage, wide input range, large input current, and system requirement into account.This paper firstly makes a comprehensive analysis of the system structure and operating principles of single-stage micro-inverters. Then, recognizing the drawbacks of traditional PI controller, Q-PR grid-connected control strategy, which could eliminate system static error, is discussed. In the discussion, amplitude-frequency characteristic is utilized to compare the performance between PI control strategy and Q-PR control strategy, and to design Q-PR controllers. Moreover, Two PV cell models are analyzed and summarized. Aiming at the problem of Perturbation and Observation can not keep the steady-state accuracy and tracking time in good condition simultaneously, a modified variable step algorithm of Perturbation and Observation MPPT is put forward. In the analysis, Matlab/Simulink is employed to simulate the theoretical models of PV cell and the modified variable step algorithm of Perturbation and Observation MPPT. Lastly, the calculations of the main parameters of the micro-inverters are described, and the parameters are demonstrated in the simulation of micro-inverter system in Saber. The results of the simulation show that the micro-inverters possess wonderful output voltage and current performance.