Design And Research Of The Distributed Photovoltaic Grid-connected Inverter

The rapid development of human society has make energy consumption leap, oil and other non-renewable energy depletion had caused global concerns.The burning of fossil fuels emit large quantities of carbon dioxide, sulfur dioxide and other gases, that cause the greenhouse effect, acid rain and other environmental issues.All those has make a serious threat to the survival and development of mankind. The development of new energy has become a trend of global energy revolution, which distributed photovoltaic power generation has become an important force in the global ecological construction and economic development. This paper mainly studies the design of distributed photovoltaic grid-connected inverter.(1)Based on the study of voltage modulation and current control method of grid-connected inverter, then analysis control strategy of distributed photovoltaic grid-connected inverter gradually. The unreasonable design of proportional control coefficient of current controller could easily lead to system instability or even damage the inverter for photovoltaic grid-connected inverter with LCL filter. Discretize themodel of inverter side inductor current feedback in three-phase photovoltaic grid inverter with LCL filter to analysis the stability of the inverter system, the precise range of parameters for proportional control can be derived. Then analysis the influence of filter inductance and capacitance on the stability of the system.(2)Analysis the PI control of grid-connected inverter in the dq coordinate,proposes an adaptive control strategies that modulation voltage is utility voltage feed forward plus a linear combination of current given and current feedback on the basis of the traditional control strategy. Its coefficients of current given and current feedback can be adjusted according to the changing grid environment. Use of Lyapunov stability theory proved that the stability of the control strategy,with Matlab simulation and practical experiment further proved that the ideal effect of control strategy.(3)The unqualified insulation resistance of photovoltaic arrays will bring about significant accidents to the equipment and personal safety, so it is necessary for photovoltaic power stations to automatically monitor insulation resistance of photovoltaic arrays. This paper proposed a new insulation monitoring scheme based on the unbalanced electric bridge, and a improved scheme based on the balanced bridge and unbalanced bridge. Took the derivative of insulation resistance calculation formula to take error analysis in theory, and use Matlab simulation setting values of imbalance resistance.(4)According to the application of configuration touch screen in photovoltaic grid connected inverter, the main interface, main function interface and anti interference design of the touch screen are described.The control strategy of grid-connected inverter, insulation resistance on-line monitoring and configuration of touch screen monitor designed in the paper all through the strict test and verify experiment on platform, achieved the expected design requirements, comply with the relevant national standards. An adaptive control strategy is presented to automatically adjust the control parameters according to the grid environment change, can improve the inverter output current waveform; The two schemes of online insulation monitoring can detect the values of insulation resistance of the DC bus and locate the fault branch accurately, reduce the voltage fluctuation in the process of the measurement, and the relative measurement errors can be controlled within 5% within a certain range, that improves the security and stability of the system operation. The design of touch screen can communication with inverter normally, and has certain anti-interference ability.