The Research On Nonisolated Single-phase Grid-connected Photovoltaic Inverter

Nowadays, on account of the problems of environmental pollution and exhaustion of energy resources becoming worse and worse, exploring and using of new energy become more and more important. Solar energy is one of the most clean, practical and large scale regeneration energy resources. The whole world focuses on the use of photovoltaic (PV). The PV grid-connected system will be the main utilization of solar energy, so it will be developed rapidly. The inverter is the last or the only one power converter stage of grid-connected PV station, whose efficiency and reliability will influence the performance of the whole system. According to different standard, the structuce of the grid-connected photovoltaic inverter is divided to many kinds. This article mainly studies nonisolated single-phase grid-connected photovoltaic inverter.This article first summarizes the development situation of grid-connected photovoltaic system and analyses the influence of the current international financial crisis on photovoltaic industry. Secondly, the characteristics of the main PV inverters on the current internatinal market are analyzed and the arrangement of PV arrays in grid-connected photovoltaic system is summarized. Whereafter, the common-mode current of the different PWM modulation modes is analyzed based on the single-phase full bridge topology in nonisolated grid-connected photovoltaic system. The condition that can avoid the common-mode current is pointed out. The influence of the different filtering patterns on the common-mode current is analyzed. The practical topologies that could avoid the common-mode current are listed out and a new topology is proposed. The power losses in the studied topologies are compared.The causes of DC current injection into the grid from grid-connected PV inverter are analyzed. The DC current could lead to the Power Transformer DC Biasing. On this base, the approaches to reducing the DC current injection are summarized and it points out that the half bridge could reduce the DC current injection. The PI controller is usually adopted in controlling the grid-connected current in Engineering. In the theory, the PI controller is unable to achieve zero steady-state error control, so the P+Resonant(PR) control which can achieve zero steady-state error is briefly analyzed. Finally, the approaches to reducing the common-mode current and the DC current injection are verified on a 1.5kW experimental prototype...