Research On DC-Module-Based Photovoltaic Grid-Connected Inverter

In recent years, solar photovoltaic power generation technology isdeveloping rapidly, which has become one of the world’s fastest developingnew energy sources. And the building integrated photovoltaic (BIPV) powergeneration system is a trend of the future, but the PV modules in this systemare easily covered by the surrounding buildings and trees, which can form apartial shadow, the hot spot phenomenon may appear when the traditionalcentralized structure and string structure work under this conditions, whichcan seriously affect the life and conversion efficiency of PV modules.Therefore, this paper takes the DC-module-based photovoltaic grid-connectedpower system which is suitable for the BIPV system as the research object,and study the DC/DC converter topology of DC module, MPPT controlstrategy, DC/AC grid-connected control strategy in depth.A front-end DC module based on the flyback converter is designed, whichhas the advantages such as simple structure, high voltage gain, low voltageripple, easy to parallel, electrical isolation between input and output, etc. Andits operation principle was analyzed in detail, the small-signal mathematicalmodel based on state-space averaging method was established, the snubbercircuit of leakage inductance was analyzed, and the design method of thecircuit parameters was given.Based on the analysis and comparison of the conventional perturbationand observation method and variable step size perturbation and observationmethod, a hysteresis-comparison-based variable-step perturbation andobservation method was proposed, which eliminated power oscillation nearthe maximum power point and power misjudgment by hysteresiscomparison, solved the contradiction between tracking accuracy and speed byvariable step.A double-closed-loop grid-connected control strategy composed of DCbus voltage external loop and grid-connected current inner loop wasresearched and design. A grid-connected inverter system structure of double closed loop control was analyzed in detail, and the voltage external loop,current inner loop control block diagram and the design method of controllerparameters based on the pole placement method was given, based on theanalysis of grid-connected inverter mathematical model. In order toenhance the anti-interference ability of the system, the voltage feedforwardlink was introduced in current inner loop, which can completely eliminate theinterference introduced by the grid voltage fluctuations. Experimental resultsdemonstrate the feasibility of the scheme.A DC-module-based photovoltaic grid-connected power systemexperimental platform was built, the corresponding hardware and softwarewere designed, and the experiments were carried out according to the schemeproposed in this paper, the experimental results demonstrate the feasibility ofthis proposal scheme.