Research On Single-stage Boost Inverter For Grid-connected Photovoltaic System

With the growing global energy crisis and the worsening of the natural environment,development and utilization of clean renewable energy, especially solar energy, has won moreattention around the world. Solar energy has become one of the main forms of new energy.Based on the background of solar photovoltaic power, this paper descipts the the significance anddevelopment status and trends of the photovoltaic power generation, overviews the development ofthe photovoltaic power generation technology. As a key component in grid-connected PV systems,grid-connected inverter’s topology and control strategy are becoming a current research foucus.Considering the limitations and shortcomings of the traditional voltage source inverter, a novelgrid-connected PV system based on single-stage boost inverter is proposed in this paper. Comparedwith traditional voltage source inverter, single-stage boost inverter(SSBI) adds a boost network withcoupled inductor, uses the shoot-through zero-vector to achieve controllable boost and inversion onone stage, and can adapt to the situations where input voltage changes in a wide range. These canmeet the requirements of the photovoltaic power generation.This paper firstly introduces the topology, equivalent circuit and operating principle of thesingle-stage boost inveter. Then, the boost characteristics of SSBI are analyzed in detail and thecoupled inductor is designed. Secondly, this paper studies on improved SPWM and SVPWMmodulation strategy for the SSBI. By summarizing the advantages and disadvantages of the dc busvoltage control methods, a variable capacitor voltage control method is proposed. Thirdly, the controlstrategy of SSBI applied to grid-connected PV system is studied, which contains grid current loop, dcbus voltage loop and maximum power point tracking loop. Based on the mathematical model, the gridvoltage oriented control strategy is presented, which makes the active and reactive current in dqcoordinate reference frame controlled respectively. Then, an improved variable step size perturbationand observation method of maximum power point tracking control stategy is discussed. The systemsimulation model in Matlab/Simulink is built and the simulation results show that the strategy iscorrect and feasible.Finally, a1kW prototype of single-stage boost inverter applied to grid-connected PV system isbuilt up, and control program are written in the software environment with the Freescale’s DSP chipMC56F8335as the core of the system. What’s more, independent and grid-connected experiments arefinished to verify the analysis is correct, which also show that the SSBI has a good performance andthe system can control dc bus voltage flexibly, output high quality grid current and track the maximum power of PV array.