Research And Design Of Single-phase Photovoltaic Inverter

The investment in green energy is increased in lot of nations because of the severe global energy problems. Solar energy is one of the most important green energy and it is of particular advantages and bright potential markets. Photovoltaic power generation is selected as a new method using solar energy, and there is great potential in power generation. Photovoltaic inverter is a key part of the Photovoltaic power generation system. Its efficiency, quality of power output and reliability are the key factors which affect the performance and investment for the system. The monophase Photovoltaic inverter is investigated, and3KW Photovotaic inverter is designed as well. Moreover, software is also investigated and developed.This project roots in a development project of digital Photovoltaic inverter. A digital Photovoltaic inverter is developed and the main contents of the project are listed as follows:Firstly, the topological structure of the main circuit in the Photovoltaic inverter is investigated, and advantages as well as disadvantages are compared. A two-level non-isolated topological structure of the main circuit is selected according to the requirements of the project. There are two control approaches in two-level main circuit structure:"two-level independence" and "double closed loop". The double closed loop method is selected in the project by comparing and analysing the two approaches.Secondly, the characteristic curve of the solar panel is analysed and couple of normal maximum power tracking method is discussed. The project focuses on the incremental conductance algorithm, improves the method, introduces the step width changing and threshold setting methods, and develops the software coding.Thirdly, the control method of the backward stage inverter bridge is analysed, the hysteresis current method, bipolar SPWM modulation method and monopolar SPWM modulation method are introduced and compared. In the end, the monopolar SPWM modulation method is selected as the control method for inverter circuit according to the system in the project. In the monopolar modulation, the grid-connected current phase is locked according to the zero crossing point which depends on the voltage of the urban grid. However, the grid-connected current lags behind the voltage because of the feature of the resistance and inductance in the grid and filter. This leads to the mandatory phase locking problem in the connected grid, and zero point pulse of the grid-connected current is the key feature. An innovation point is proposed according to the problems mentioned above:grid-connected current phase correction method which solves the mandatory phase changing problem by correcting the start address of the sine wave meter pointer.And design the Anti-islanding method base on the lock method in the system.At last, the simulating and modelling are given according to the relative blocks, and the arguments are demonstrated by comparing the simulated wave. Moreover, the coding is done depending on the TMS320F2812digital control chip.The results are given to demonstrate the efficiency of the proposed control strategy at last, so as the conclusion and the future work.