Research On Transferring Control Method Of Micro-grid Double Mode Inverter

The energy problem causes the attention of domestic and foreign. Many scholars focus on research in the field of smart grid. The micro-grid brings new power revolution after smart grid. The micro-grid is mainly in the stage of experiment and demonstration. Countries are trying to develop the micro-grid industry. Domestic policies also support the development of micro-grid. Micro-grid market will expanding to new rural construction and household micro-grid.This paper studies the composition and structure, various function of module, running characteristic, various control method of three-phase inverter and seamless transfer in micro-grid. The control method of three-phase inverter and seamless transferring strategy of double mode inverter in micro-grid are analysed deeply. The control method for three-phase inverter usually uses the traditional linear control methods, including PQ control method, V/f control method, droop control method, and so on. These methods are always used on one mode and only stable near the equilibrium. However nonlinear and uncertainty are complex in micro-grid. These methods can’t guarantee the stability in large range. Thus the back-stepping control(BSC) is used in this paper for three-phase inverter.Different math models are set up for seamless transfer between grid-connected mode and grid-disconnected mode. Simulation platform is set up. Controllers of grid-connected mode and grid-disconnected mode are designed with the BSC method. The design process considers many uncertain factors. Finally, the transferring control strategy of double mode is put forward for seamless transfer in micro-grid. According to the result of voltage and current, load shedding and harmonic suppress, the simulation results verify the effectiveness of the strategy in stand-alone mode and multiple machine mode. The results also verify the superiority of the strategy compared with PQ-V/f control strategy and droop control strategy. The proposed strategy solves the seamless transfer problem and it has less sudden voltage and current. It solves the handover failure problem. The strategy responses quickly. It has no power oscillation and has stronger robustness. It also reduces the harmonic distortion. Thus quality of electric energy is improved.