Research Of Technology In PV-connected System Based On Dual-stage Soft-swithching Inverter

A multitude of problems were consumed in the world by using conventional fossil energy.Among them, energy crisis and environmental pollution are the two most prominent issues, so new energy power generation into the line of sight of the various countries. Photovoltaic grid connected power generation has many advantages, it has become one of the main energy sources in 21 th Century. However, due to the high cost of power generation, photovoltaic grid connected power generation is still unable to be widely used in the present. So it is an urgent problem to improve the photoelectric conversion efficiency of photovoltaic cells and improve the conversion efficiency of the grid connected converter. If the conversion efficiency of the converter is improved, more power output can be obtained.First of all,two-stage soft switching converter topology which is applied in photovoltaic grid connected system was introduced, soft switching technology used in photovoltaic power converter can increase the power density system to achieve light weight and miniaturization.Among them, before the class type of boost converter DC/DC converter using a modified,easy to realize soft switching function, high step-up ratio for two-stage grid connected PV system; using improved unipolar double lotus synthetic inductance DC/AC converter. By comparing the performance of soft switching with different DC/AC topologies, the topology is not easy to be balanced, and the auxiliary device has small current stress, and the reset of exciting current is easy to implement. Then, in order to verify the performance of the soft switching of the topology, the principle of the topology is analyzed.Secondly, three classical maximum power point tracking algorithm was proposed, and this artical analyzes there for the algrithm error. The problems existed in the conductance increment method of fixed step size and the traditional variable step size incremental conductance method. An improved variable step incremental conductance method is proposed to optimize the scaling factor. And the MPPT control algorithm is established, and the PSIM software is used to simulate the algorithm. After analyzing the simulation results, simulation proved the effectiveness of this algorithm.And then, the two stage photovoltaic grid connected converter has two different control strategies. This paper introduces the principle of the two MPPT control strategies. And select the more suitable for the photovoltaic grid connected system in front of the use of MPPT control strategy.Finally, this paper will use the improved variable step conductance incremental algorithm to control the two stage photovoltaic grid connected converter using PSIM software to simulate and analyze the output of the simulation waveform. It is proved that the converter has the function of stabilizing the grid connection in the drastic changing environment.