The Research For Photovoltaic Grid-connected Converter Based On DSP

With continuous rising of the global economy and people livings standard as well as consumption of the fossil fuel resources, great concerns on future energy supply and environment sustainability have been developed for the public. In fact, all the above concerns have become the bottleneck of our future development. Therefore, improving the efficiency of current energy infrastructures and seeking alternative energy sources become the imperative tasks for nowadays engineers. Solar energy is considered as one of the supplement candidates for future energy supply due to the clean energy conversion process and less environmental impact. However, this conversion process is dominated by solar inverter process which is the main apparatus for solar energy conversion. The objective of this research is to develop a solar inverter, which is capable to operation in grid-tie and islanding conditions. Issues of system structure, circuit topology, grid-tie control, phase-lock loop and islanding detection will be discussed in the research.Firstly, upon discussion of photovoltaic principles and panel output characteristics, several MPPT algorithms will be discussed and evaluated for performance and implementation complexity. An improved variable step MPPT algorithm will be proposed in this research to further improve the solar system efficiency.On the circuit level, the system structure and individual stage topology will be discussed, and a two stage solar inverter structure is proposed. The boost stage is chosen as the front-end stage, and boost stage modeling and pass component selection will be investigated.Analyzed the main circuit structure and operated principle of the converter, and give the simple introduction to the structure of the control circuit and proposed two stage type topology structure. The previous stage adopts the BOOST transform machine to match the different input voltage, and gave parameter selection of components in circuit, and verified the rationality of design through imitation and experiments.Based on the analysis foundation of the cycle time, the design elaborates the control object of converter, summarize the conditions when it works on the connected-net state, and carries contrast analysis on the control strategy popular at present. The algorithm adopted in this design is the SPWM based on current control, and the algorithm has the merits such as switch frequency stationary, clear physical meaning and convenient carry out etc, assures that outputting waveform is good and response quickly.Later on, give the introduction for some problem that have to work out in connected-net system such as digital PLL and isolated island effect etc. This text carried on the meaning and correlation standard of isolated island effect, analyzed the reason generate the effect and explained its harm.At last, adopt DSP56F8346which is the production of FREESCALE company as the control chip, design and complete the experiment model machine carry on1KW, and the result of experiment express that the design is as satisfied for the control strategy and the hardware, the system can run safely and stably.