| Solar energy is the most clean, safe and reliable energy in the future, driven by the strong driving force of technological progress and the gradual perfection of regulations and policies, PV industry enters the stage of rapid development.The main components of the photovoltaic off-grid & grid-connected system include solar cell module,MPPT(Maximum Power Point Tracking) charging controller,lead acid battery and photovoltaic off-gird & grid-connected inverter. Photovoltaic off-grid & grid-connected inverter take off-grid inverter as the main, at the same time, with the AC input, network output,UPS and other additional functions. The off-grid inverter of photovoltaic off-grid & grid-connected inverter is carried out, the main research work is as follows:(1) The topology structure of the main circuit of photovoltaic off-gird & grid-connected inverter is presented, the working principle and working mode are explained in detail,the theoretical basis and objective principle of selecting the parameters of the key components such as the MOSFET gate drive resistance, the two order LC filter network, etc. the calculation formula of the key parameters of the main circuit of the photovoltaic grid connected inverter is derived and provided.(2) A unipolar & frequence multiplication SPWM(sinusoidal pulse width modulation) is introduced, through detailed analysis, and then the SPWM pulse signal mathematical relationship between the MOSFET gate and Inverter bridge output side is obtained. With the aid of MATLAB/Simulink computer simulation software,the analysis proves that it has obvious advantages in restraining the waveform distortion, reducing the harmonic content, improving the quality of the waveform and improving the efficiency of the inverter.(3) The frequency characteristics of photovoltaic off-grid & grid-connected inverter is studied and analyzed in detail in this paper, mathematical modeling of the main circuit topology, analysis of small signal system using state space averaging method and adopting improved PI control regulative compensator, the digital control of the system is realized.With the aid of the MATLAB/Simulink computer simulation tool and Freescale semiconductor company’s new generation of products MK60DN512ZVLQ10 hardware platform for specific experiments.Simulation curves and experimental results show that:the design of photovoltaic off-grid & grid-connected inverter can meet the practical needs of different loads. |
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