Frequency And Voltage Control Of Interconnected Micro-grid Systems

With the ever increasing global demand for energy,the distributed generation and microgrid having the characteristic of non-traditional energies of photovoltaic,wind,tide,geothermal,etc have been rapidly developed and promoted.And the application of power electronic technologies have improved the quality of electricity and the efficiency of power supply,as well as render the interconnection of the distributed generation or microgrid possible.The microgrid can be operated in parallel with the utility grid,or can be operated independently,and,It could also operate in the mode of island in the form of multiple microgrids interconnection.From the perspective of safety and reliability,microgrid interconnection has more advantages.To the multiple microgrid system,its internal load changes and the output power fluctuation of micro-source will cause the system frequency and voltage offset as well as the active power of the tie-line to deviate from the planned value.Therefore,it is necessary to take corresponding measures to effectively control the operation of interconnected microgrid.In this paper,will study the frequency and voltage control of interconnected microgrid systems with two different tie-line.For the interconnected microgrid system that connected by AC tie-line,a power coordination control strategy is proposed,to control the frequency and voltage of the interconnected microgrid through control the micro-source active power and reactive power within the microgrid.According to this strategy,the microgrid frequency can be adjusted near target value when microgrid's power backup is sufficient,and the active power of the tie-line can be restored to the command value;at the same time,the voltage deviation left by the droop control of the micro-source is eliminated,and the reactive power within microgrid is suppressed.For the interconnected microgrid system that connected by DC tie-line,a frequency and voltage adjustment strategy based on tie-line power control is proposed.The microgrid power manager calculates the unbalanced power of each microgrid in real time,introduces the active power and the reactive power deviation into the micro-source control strategy,adjusts the generation power output,and set up the power reference values of the converters at the sending and receiving terminals.The research results prove that the proposed strategy can effectively control the frequency and voltage of the interconnected microgrid system connected by the DC tie-line,and maintain the transmission power of the tie-line at the specified value.