Study On Common-mode Leakage Current And Reactive Power Compansation Of Single-phase Photovoltaic Grid-Connected Inverters

The inverter is an important part of the photovoltaic power generation system, and a core in the development and utilization of solar energy. To ensure reliable photovoltaic power generation system operation, traditional grid-connected inverter uses the isolation transformer. But the use of isolation transformer will result in a large system size and weight, low efficiency and high cost. The transformerless grid-connected inverter has already overcome the shortcomings, and it has become a hot research.The removal of the transformer result in common mode leakage current which can cause safety and electromagnetic interference problems. Hence, it is important to solve the problem of leakage current. In this paper, taking non-isolated single-phase full bridge topology as an example, a common-mode equivalent model of it is analyzed. And the common-mode current of the different PWM modulation is analyzed. The way to eliminate common mode leakage current has been summarized. And then, four new transformerless PV inverter topologies are researched in this thesis. The common-mode characters of four improved topologies are compared in this paper by simulation.In order to improve the efficiency of the system and avoid shoot-through issue, the paper focuses on a new dual buck full-bridge inverter. It has the advantages of high input DC voltage utilization, no shoot-through issue and lower leakage currents. The operation principle of the new dual buck full-bridge topology is analyzed, the main parameters is designed, and the efficiency optimization is also dealt with. Experimental and simulation results show that the suppression of common-mode current and efficiency of the new dual buck full-bridge topology superior to that of H6inverter.German standard VDE-AR-N4105has already been updated in August2011, and in this clause the requirement of reactive power injected into grid is proposed. However, in order to eliminate leakage current and achieve high efficiency, majority of non-isolated grid-connected photovoltaic inverters employ uni-polar pulse-width modulation, which may result in current distortion at zero crossing. Therefore, it increases the THD of grid-connected current and it is hard to meet with the requirement of±0.01displacement factor accuracy, In this paper, the new dual buck full-bridge topology, taken as an example. The reason of current distortion at zero crossing when compensating the reactive power has been analyzed, and a kind of modulation strategy is proposed to eliminated this distortion. The effectiveness of the proposed method is verified by simulation and experiment.