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Aiming at the leakage current problem of single-phase transformerless photovoltaic(PV) grid-connected inverters, the recent proposed topologies are classified and reviewed. These topologies are divided into half-bridge type and full-bridge type. The topology characteristics of transformerless PV inverter are analyzed. This paper presents some of transformerless PV inverter topologies and discusses the evolution laws among various topologies to clarify the interrelationship between them. Furthermore, according to the evolution laws, a new topology is proposed. Finally, Simulations and experiments compare leakage current suppression capability of the proposed topology, H5 topology and HERIC topology.

A new nonlinear compact LED model is presented in this paper. The model is useful in the design stage of LED driver system. The parameter extraction procedure is presented step by step. Since the power of a single LED unit is very low, manufacturers often arrange LED units in the form of an array named LED module. On the basis of theoretical I-V characteristic curve of the LED module, the electrical performance of LED module can be tested according to the rated parameters provided by its manufacturers. Five fitting methods are used to obtain the fitting curves. The sum of squares due to error (SSE) and the coefficient of determination (R-square) are compared to choose a better fitting curve. Six terms gaussian fitting method, which has optimal fitting performance among the five methods, is chosen to construct the nonlinear mathematical model of the LED module, and then the simulation model is built with MATLAB/Simulink. A Boost converter simulation circuit adapts this model, and a 25 W dimming prototype is designed to verify the validity of the model. The simulation and test results show that the error of the model is small, and it meets the requirements of practical application.