Control Strategy And Research For Smooth Switching Of Microgrid

In order to solve the shortage of energy in our country, we must gradually increase the use of new energy, such as photovoltaic, wind power and tidal energy, increasing the proportion of renewable energy. Since the operation mode of micro-grid is convenient and flexible, operation with the power grid, reliable support the power grid; at the same time it also can running in island state to ensure supply stable power for locally important load. When micro-grid running between grid and island state, the change of voltage, frequency current phase sequence and phase angle matching question will affect the stability and safety of micro-grid. Therefore, how to ensure a smooth and active handover process in the micro-grid is an important issue, but also is the focus content of my study.Firstly, analysis the control method of micro power in the micro-grid smooth handover system: PQ control, V/f control and droop control. PQ control method can ensure each micro-power constant power output, but can’t guarantee stable voltage and frequency when the micro-grid switching to the island; V/f control method can ensure stable frequency and voltage micro-grid switching to island, but can’t guarantee the output of each micro-power, thus resulting in low energy efficiency; droop control strategy belongs to droop when micro-grid switching the operating status, deviation from the normal range switch process is not smooth, caused by voltage and frequency to a certain extent. Through analysis and comparison of these three control strategies’ advantages and disadvantages in the micro-grid, islanding and smooth handover process, this paper modified micro-power V/f droop control, through analysis of this control method, it can ensure the output of micro-power, ensure that the voltage and frequency of the smooth handover process, while ensuring a stable voltage and frequency of micro-grid system and a reliable power supply to local loads.Subsequently, through research and analysis of two overall control strategy of micro-grid smooth switching system: the master-slave control and peer control, through compare the advantages and disadvantages of the two control strategies, submit a comprehensive control strategy of micro-grid smooth handover. When the micro-grid is on power grid, the various control units using PQ control methods to ensure the power output; during the switching, energy storage system using the improved V/f droop control to suppress and regulate voltage and frequency, the rest unit use the PQ control. Finally, set up the simulation model in matlab/simulink software platform, validated the integrated control strategy by simulation: on the one hand it can ensure a stable voltage and frequency in the switching smooth process of micro-grid; on the other hand can ensure the greatest degree output of micro-power; while also reducing the number of switching between control strategies.