Micro-grid Seamless Switching Control Strategy Based On Inverter

Energy crisis and environmental problems coupled with the traditional large-scale power systems increasingly apparent structural aging, low energy efficiency and other defects,make people think about the use of renewable energy.Due to environmental protection, energy conservation, economic and other advantages,distributed generation is widespread concerned,micro-grid is the most effective and efficient form of distributed generation and become one of the hot in power industry research in recent years.The mission of micro-grid is to provide clean, reliable, high-quality electricity services.Parallel operation between the micro-grid and wide grid can not only save investment, improve power quality, but also ensure the stability and flexibility of the power system.Islanding mode and network mode are two modes of micro-grid operation,in the switch of two modes,The difference of hardware and software clock results the asynchronism of inverter control mode switching and operation mode switching,and ultimately led to current and load voltage shocks.Thus,seamless switching can not attained.In the paper,firstly,the principle of solar photovoltaic, wind power, micro-turbines and battery is discussed,and the appropriate mathematical models are established.Secondly, based on the discussion of inverter control principle of solar photovoltaic, wind power, micro-turbines, and batteries, PQ controller, V/f control and weighted voltage and current control strategy are proposed. A micro-power and control simulation model is built.And the validity and feasibility of the control strategy is verified.Finally,the model of the entire micro-grid and control system is established and model of micro-grid dual operation mode switching is simulated in PSCAD/EMTDC.A weighted control algorithm is proposed for problem in the dual operation mode switching. On the basis of the inverter controller loop control by changing the value of the weighting factor, and net transition process by adding the weighted voltage control, adding the transition process from the current net weight control. After changing control strategy, the current network can be suppressed and shock, stable load voltage reaches the final double micro-grid seamless switching operation mode.