Research On Photovoltaic Grid-connected Inverter And Its Control

In Photovoltaic Grid-connected system, inverter is key part, whose efficiency and reliability will influence the performance of the whole system. By comparing topology and configuration of several programes in small photovoltaic grid-connected system, single-stage photovoltaic grid-connected inverter without transformer is selected to study.The target of control in photovoltaic grid-connected system is ensuring the output current of the inverter circuits to be the sine waves of quality, with the same frequency and phase as the grid. By analyzing the several common control algorithms of inverter, adopt hysteresis current control algorithm to make the output current of inverter tracking the grid. As it is well known, the hysteresis control is characterized by unconditioned stability, very fast response, and good accuracy. On the other hand, the basic hysteresis technique exhibits also several undesirable features, such as variable switching frequency and heavy interference among the phases in case of three-phase systems with isolated neutral. By analyzing the hysteresis current control algorithm and the reasons for switching frequency fluctuations, provide two algorithms of stabilizing the switching frequency, the first is based on integration and the second is based on least squares method. By simulating based on MATLAB, the result proves the two algorithms not only maintain the advantage of traditional hysteresis current control algorithm, but also achieve a stable switching frequency.For using the constant frequency hysteresis current control algorithm in case of three-phase systems with isolated neutral, by analyzing the traditional three-phase current decoupling control algorithm, a new decoupling algorithm based on line current is provide in this paper. The simulation result shows that the new constant frequency hysteresis current control algorithm is available in case of three-phase systems. The output current of inverter is the sine waves of quality, with the same frequency and phase as the grid.