Development Of The Mini-series Converter Based On Z Sources For Photovoltaic Grid-connected System

The distributed cascade micro converter is used in photovoltaic grid-connected-connected system(Photovoltaic Grid-connected Systems,PVGS). The system is based on the photoelectric effect. The Photovoltaic converts light into electric energy and converts direct current into alternating current by the inverter and incorporated into a large grid-connected. The output power and the output voltage of PV present the nonlinear relationship. The PV module is added to a converter. It makes the power output of the PV module maximum. Because the conventional DC/DC topologies have some deficiencies, they a re unable to meet the high voltage gain and prevent the hot spot effect. So this paper presents a series micro converter based on Z-source with a precharge resistor. It can conquer the abuse of the traditional topology.This paper briefly introduces the three commonly maximum power point tracking(MPPT) algorithms and describes the shortcomings of the three algorithms first. Then, a variable step-size batch scanning algorithm based on P-Vcurve is proposed. Through modeling and analysis, it verified that this algorithm not only has high accuracy and tracking speed advantage and can appropriate the step according to the actual state of the environment to achieve that the scan time is prolonged or reduced for improving system stability. This paper describes the control algorithm of the three-phase grid-connected inverter. This algorithm makes that the voltage of DC bus and the output waveform are better.This paper analysis the theory of the PV serial micro converter,based on DSP2812 controller, IGBT module in detail and developed the physical model, it comprises PV module, DC/DC converter module based on Z-source, three-phase inverter module and the correspinding control module. In this paper, the system used the tandem structure model based on the DC bus voltage. At last, according to building the physical models, a series of experiments testing were conducted, it shows that the grid-connected system based on Z-source can achieve the MPPT, prevent hot spot effect and achieve grid-connected functions.