Research On Single-phase PV Grid-connected Inverter

The world we live in is facing two serious problems, energy reduction and pollution.Most countries in the world are adjusting energy structure, developing new energy and renewable energy. Solar energy industry has been developed a lot and it possibly can be the most important energy in the future. The PV inverter is a important part of the PV system.The stable, efficient and reliable PV inverter will speed up the PV system development.The original PV inverter used power frequency transformer. It is too big and heavy, so there is more types inverter to replace it. The paper designs a single-phase PV grid-connected inverter. The inverter has two converters, that is simple, efficient and easy to control. The first converter is Boost converter, that step-up the cell voltage. After Boost converter, it uses a capacitance to make the voltage stable. The second converter is full bridge inverter, which changes the DC into AC. It uses the LCL filter to reduce the current pulse. Compared the L filter with LCL filter, it is found that the LCL filter has better functions. The LCL filter has a resonance problem, and the paper designs scheme of active damping and passive damping to suppress the transient resonance of LCL filter. The active damping scheme does better to suppress the transient resonance. The paper designs that the boost chopper changes the output voltage of the PV cells by adjusting the duty cycle to achieve the maximum power point. The inverter control contains inner current loop and external voltage loop. The external voltage loop uses the PI regulator make the DC stable, and the inner current loop control uses the PR regulator make the grid-connected current and grid voltage same phase. Through analyzing the mathematical model of the common mode current, it is found that the bipolar SPWM modulation can suppress the common mode current. Including the grid-connection requirements. the PV system has to design a islanding detection methods. The paper designs a active frequency shift to detect islanding. The PR controller can easy to suppress the 3rd harmonic, 5th harmonic, and so on.The paper simulates the PV system in MATLAB, and the result shows the system that it designs stable, efficient and reliable. The paper does an experiment on the inverter, and the experiment shows the PR controller can follow the sine wave without error.