Research On Control Strategy In Photovoltaic Grid-Connected Inverter With LCL Filter

The global energy becomes more and more serious, it’s hard to meet people’s growing demand just based on the combustion of fossil fuels. The development of sustainable energy received more attention, the solar energy with its unique advantage get more attention. PV-grid inverter is the core part of PV system. Based on three phase two levels of PV-grid inverter, mainly study two core problems, MPPT and the synchronization of grid current and power voltage.The output current and voltage of PV cells also change, the key to keep it working efficiency is to work under maximum power point. Based on the analysis of disturbance observation method, adopt a new method to achieve the maximum power point tracking, decrease the volume and cost. The method is verified by Matlab simulation.The inverter adopt LCL filter, but the zero resistance caused by resonance may affect the stable. For the zero resistance caused by the LCL filter, a weighted average current control scheme is adopted. However, it has coupling, and difficult to control. The current loop adopts a feed forward decoupling scheme and is adopted to alleviate the problem. LCL grid inverter based on weighted average current control is sensitive to the change of grid inductance, based on the traditional specific frequency harmonic injection method, adopt a new method of grid inductance measurement without harmonic injection. Through sampling grid current and capacitor voltage and inductance twice. It can detect the value of grid inductance accurately, tracking the range of grid inductance quickly.With STM32F103RBT6 micro controller as the master control chip, design the hardware and software. Hardware part includes the main circuit, current detection and protection circuit, DC bus voltage circuit, the zero crossing detection circuit, power circuit and so on. the software part includes GPIO modules, SPWM module, timer module, the main function module, etc.Finally, the prototype achieves the same frequency and phase between grid current and grid voltage. Analyze the shortage of the system, and proposed the next plan.