Study On Grid-connected Micro-photovoltaic Power System With The Application Of A Novel Control Method

With the economic globalization, energy shortage and environmental pollution become a growing problem, so research and utilization of new energy power generation is imperative. The solar energy is a green renewable energy, with its universality, clean, permanence and great, etc., and has broad prospects for development. Because environmental conditions such as temperature and light have a greater impact on solar energy, so the PV power inverter has high requirements on efficiency and reliability each PV module with a micro-inverter, can effectively improve system efficiency and reliability and will become the future trend of development.Multi-level inverter system can effectively reduce harmonics to improve power quality, and can significantly reduce the switching frequency of a single tube to reduce the switching losses. Therefore, for reducing the tracking error and switching frequency of the system, the study on control methods for multi-level inverter has some practical significance.In this paper, a new type control method is proved for multi-level hysteresis tracking.The method gets the dynamic logic of its distribution for multi-level tracking, by controlling the signal.of the upper and lower threshold. It can make zero tracking average error, but also reduce system switching frequency, to reduce harmonic of the output PWM waveform. At the same time, this paper builds single-phase inverter simulation system on MATLAB/Simulink platform to achieve three-level tracking simulation.This paper also has a study on system topology for miniature photovoltaic inverters. The direct current of a single PV modules turns into alternating current with public frequency to send the power back to the grid. To achieve electrical isolation, the system uses a multi-stage grid-connected inverter with a high-frequency transformer, which is small and light. The new three-level tracking control method is applied to the system, which makes the switching frequency and the system harmonic content be reduced. At the same time, by the use of the maximum power point tracking algorithm, the system has improved the output power of PV module. Through the grid-connected algorithm and multi-level tracking control algorithm, the system can achieve unity power factor back to grid. In addition, the use of soft-switching technology in the tracking control algorithm can get further reducing of the switching losses and improve efficiency.Finally, the STM32series of ARM and MAX Ⅱ series of CPLD are used as core digital control chips. The experimental photovoltaic inverter system with250W is completed. This paper supplies the details of design principles and parameters about the main circuit and control circuit, and shows preliminary experiment results with low DC input voltage to prove the accordance with the theoretical analysis.